Introduction #

This article is a basic tutorial for the programming language Odin. This tutorial assumes a basic knowledge of programming concepts such as variables, statements, and types. It is recommended to read the Getting started with Odin guide.

Hellope! #

To begin this tour, let us start with a modified version of the famous “hello world” program:

package main

import "core:fmt"

main :: proc() {

Save this code to a .odin file, then compile and run it using odin run <dir>. For the current directory:

odin run .

The run command compiles the .odin file to an executable and then runs that executable after compilation. If you do not wish to run the executable after compilation, the build command can be used.

odin build <dir>

Odin thinks in terms of directory-based packages. To tell it to treat a single file as a standalone package, add -file, like so:

odin run hellope.odin -file

Lexical elements and literals #

Comments #

Comments can be anywhere outside of a string or character literal. Single line comments begin with //:

// A comment

my_integer_variable: int // A comment for documentation

Multi-line comments begin with /* and end with */. Multi-line comments can be also be nested (unlike in C):

	You can have any text or code here and
	have it be commented.
		NOTE: comments can be nested!

Comments are parsed as tokens within the compiler. This is to allow for future work on automatic documentation tools.

String and character literals #

String literals are enclosed in double quotes and character literals in single quotes. Special characters are escaped with a backslash \.

"This is a string"
'\n' // newline character

Raw string literals are enclosed in single back ticks.


The length of a string can be found using the built-in len proc:


If the string passed to len is a compile-time constant, the value from len will be a compile-time constant.

Escape Characters #

  • \a - bell (BEL)
  • \b - backspace (BS)
  • \e - escape (ESC)
  • \f - form feed (FF)
  • \n - newline
  • \r - carriage return
  • \t - tab
  • \v - vertical tab (VT)
  • \\ - backslash
  • \" - double quote (if needed)
  • \' - single quote (if needed)
  • \NN- octal 4 bit character (2 digits)
  • \xNN - hexadecimal 8 bit character (2 digits)
  • \uNNNN - hexadecimal 16-bit Unicode character UTF-8 encoded (4 digits)
  • \UNNNNNNNN - hexadecimal 32-bit Unicode character UTF-8 encoded (8 digits)

Numbers #

Numerical literals are written similar to most other programming languages. A useful feature in Odin is that underscores are allowed for better readability: 1_000_000_000 (one billion). A number that contains a dot is a floating point literal: 1.0e9 (one billion). If a number literal is suffixed with i, it is an imaginary number literal: 2i (2 multiply the square root of -1).

Binary literals are prefixed with 0b, octal literals with 0o, and hexadecimal literals with 0x. A leading zero does not produce an octal constant (unlike C).

In Odin, if a number constant can be represented by a type without precision loss, it will automatically convert to that type.

x: int = 1.0 // A float literal but it can be represented by an integer without precision loss

Constant literals are “untyped” which means that they can implicitly convert to a type.

x: int // `x` is typed as being of type `int`
x = 1 // `1` is an untyped integer literal which can implicitly convert to `int`

Variable declarations #

A variable declaration declares a new variable for the current scope.

x: int // declares `x` to have type `int`
y, z: int // declares `y` and `z` to have type `int`

Variables are initialized to zero by default unless specified otherwise.

Note: Declarations have to be unique within a scope.

x := 10
x := 20 // Redeclaration of `x` in this scope
y, z := 20, 30
test, z := 20, 30 // not allowed since `z` exists already

Assignment statements #

The assignment statement assigns a new value to a variable/location:

x: int = 123 // declares a new variable `x` with type `int` and assigns a value to it
x = 637 // assigns a new value to `x`

= is the assignment operator.

You can assign multiple variables with it:

x, y := 1, "hello" // declares `x` and `y` and infers the types from the assignments
y, x = "bye", 5

Note: := is two tokens, : and =. The following are all equivalent:

x: int = 123
x:     = 123 // default type for an integer literal is `int`
x := 123

Constant declarations #

Constants are entities (symbols) which have an assigned value. The constant’s value cannot be changed. The constant’s value must be able to be evaluated at compile time:

x :: "what" // constant `x` has the untyped string value "what"

Constants can be explicitly typed like a variable declaration:

y : int : 123
z :: y + 7 // constant computations are possible

For more information regarding value declarations in general, please see the Odin FAQ and Ginger Bill’s article On the Aesthetics of the Syntax of Declarations.

Packages #

Odin programs consist of packages. A package is a directory of Odin code files, all of which have the same package declaration at the top. Execution starts in the package’s main procedure.

import statement #

The following program imports the fmt and os packages from the core library collection.

package main

import "core:fmt"
import "core:os"

main :: proc() {

The core: prefix is used to state where the import is meant to look; this is called a library collection. If no prefix is present, the import will look relative to the current file.

Note: By convention, the package name is the same as the last element in the import path. "core:fmt" package comprises of files that begin with the statement package fmt. However, this is not enforced by the compiler, which means the default name for the import name will be determined by the last element in the import path if possible.

A different import name can be used over the default package name:

import "core:fmt"
import foo "core:fmt" // reference a package by a different name

Exported names #

All declarations in a package are exported by default.

The private attribute can be applied to an entity to prevent it from being exported from a package.

my_variable: int // cannot be accessed outside this package

You may also make an entity private to the file instead of the package.

my_variable: int // cannot be accessed outside this file

@(private) is equivalent to @(private="package").

Authoring a package #

A package is a directory of Odin code files, all of which have the same package declaration at the top, e.g. package main. Each .odin file must have the same package name. A directory cannot contain more than 1 package.

Organizing packages #

Packages may be thematically organized by placing them in subdirectories of another package. For example: core:image/png and core:image/tga, as subdirectories of core:image. Nesting these packages is a helpful taxonomy. It does not imply a dependency: core:foo/bar does not need to import core:foo and reference anything from it.

Control flow statements #

for statement #

Odin has only one loop statement, the for loop.

Basic for loop #

A basic for loop has three components separated by semicolons:

  • The initial statement: executed before the first iteration
  • The condition expression: evaluated before every iteration
  • The post statement: executed at the end of every iteration

The loop will stop executing when the condition is evaluated to false.

for i := 0; i < 10; i += 1 {

Note: Unlike other languages like C, there are no parentheses ( ) surrounding the three components. Braces { } or a do are always required.

for i := 0; i < 10; i += 1 { }
for i := 0; i < 10; i += 1 do single_statement()

The initial and post statements are optional:

i := 0
for ; i < 10; {
	i += 1

These semicolons can be dropped. This for loop is equivalent to C’s while loop:

i := 0
for i < 10 {
	i += 1

If the condition is omitted, this produces an infinite loop:

for {

Range-based for loop #

The basic for loop

for i := 0; i < 10; i += 1 {

can also be written

for i in 0..<10 {
// or
for i in 0..=9 {

where a..=b denotes a closed interval [a,b], i.e. the upper limit is inclusive, and a..<b denotes a half-open interval [a,b), i.e. the upper limit is exclusive.

Certain built-in types can be iterated over:

for character in some_string {
for value in some_array {
for value in some_slice {
for value in some_dynamic_array {
for key in some_map {

Alternatively a second index value can be added:

for character, index in some_string {
	fmt.println(index, character)
for value, index in some_array {
	fmt.println(index, value)
for value, index in some_slice {
	fmt.println(index, value)
for value, index in some_dynamic_array {
	fmt.println(index, value)
for key, value in some_map {
	fmt.println(key, value)

The iterated values are copies and cannot be written to.

Note: When iterating across a string, the characters will be runes and not bytes. for in assumes the string is encoded as UTF-8.

It is also possible to iterate over arrays and slices in a by-reference manner by prepending a & to the value:

for &value in some_array {
	value = something
for &value in some_slice {
	value = something
for &value in some_dynamic_array {
	value = something
// does not impact the second index value
for &value, index in some_dynamic_array {
	value = something

Maps can have their values iterated in a by-reference manner but not their keys which are immutable:

for key, &value in some_map {
	value = something

Note: It is not possible to iterate a string in a by-reference manner as strings are immutable.

for reverse iteration #

Recently a special directive was added which allows to #reverse the above mentioned range based iteration.

array := [?]int { 10, 20, 30, 40, 50 }

#reverse for x in array {
	fmt.println(x) // 50 40 30 20 10

if statement #

Odin’s if statements do not need to be surrounded by parentheses ( ) but braces { } or do are required.

if x >= 0 {
	fmt.println("x is positive")

Like for, the if statement can start with an initial statement to execute before the condition. Variables declared by the initial statement are only in the scope of that if statement.

if x := foo(); x < 0 {
	fmt.println("x is negative")

Variables declared inside an if initial statement are also available to any of the else blocks:

if x := foo(); x < 0 {
	fmt.println("x is negative")
} else if x == 0 {
	fmt.println("x is zero")
} else {
	fmt.println("x is positive")

switch statement #

A switch statement is another way to write a sequence of if-else statements. In Odin, the default case is denoted as a case without any expression.

switch arch := ODIN_ARCH; arch {
case .i386, .wasm32, .arm32:
	fmt.println("32 bit")
case .amd64, .wasm64p32, .arm64:
	fmt.println("64 bit")
case .Unknown:
	fmt.println("Unknown architecture")

Odin’s switch is like the one in C or C++, except that Odin only runs the selected case. This means that a break statement is not needed at the end of each case. Another important difference is that the case values need not be integers nor constants.

To achieve a C-like fall through into the next case block, the keyword fallthrough can be used.

Switch cases are evaluated from top to bottom, stopping when a case succeeds. For example:

switch i {
case 0:
case foo():

foo() does not get called if i==0. If all the case values are constants, the compiler may optimize the switch statement into a jump table (like C).

A switch statement without a condition is the same as switch true. This can be used to write a clean and long if-else chain and have the ability to break if needed

switch {
case x < 0:
	fmt.println("x is negative")
case x == 0:
	fmt.println("x is zero")
	fmt.println("x is positive")

A switch statement can also use ranges like a range-based loop:

switch c {
case 'A'..='Z', 'a'..='z', '0'..='9':
	fmt.println("c is alphanumeric")

switch x {
case 0..<10:
case 10..<13:
case 13..<20:
case 20..<30:

#partial switch #

With enum values:

Foo :: enum {

f := Foo.A
switch f {
case .A: fmt.println("A")
case .B: fmt.println("B")
case .C: fmt.println("C")
case .D: fmt.println("D")
case:    fmt.println("?")

#partial switch f {
case .A: fmt.println("A")
case .D: fmt.println("D")

With union types (see Type switch statement)

Foo :: union {int, bool}
f: Foo = 123
switch _ in f {
case int:  fmt.println("int")
case bool: fmt.println("bool")

#partial switch _ in f {
case bool: fmt.println("bool")

defer statement #

A defer statement defers the execution of a statement until the end of the scope it is in.

The following will print 4 then 234:

package main

import "core:fmt"

main :: proc() {
	x := 123
	defer fmt.println(x)
		defer x = 4
		x = 2

	x = 234

You can defer an entire block too:

	defer {
	defer if cond {

Defer statements are executed in the reverse order that they were declared:

defer fmt.println("1")
defer fmt.println("2")
defer fmt.println("3")

Will print 3, 2, and then 1.

A real world use case for defer may be something like the following:

f, err :="my_file.txt")
if err != os.ERROR_NONE {
	// handle error
defer os.close(f)
// rest of code

In this case, it acts akin to an explicit C++ destructor however, the error handling is basic control flow.

Note: The defer construct in Odin differs from Go’s defer, which is function-exit and relies on a closure stack system.

when statement #

The when statement is almost identical to the if statement but with some differences:

  • Each condition must be a constant expression as a when statement is evaluated at compile time.
  • The statements within a branch do not create a new scope
  • The compiler checks the semantics and code only for statements that belong to the first condition that is true
  • An initial statement is not allowed in a when statement
  • when statements are allowed at file scope


when ODIN_ARCH == .i386 {
	fmt.println("32 bit")
} else when ODIN_ARCH == .amd64 {
	fmt.println("64 bit")
} else {
	fmt.println("Unsupported architecture")

The when statement is very useful for writing platform specific code. This is akin to the #if construct in C’s preprocessor. However, in Odin, it is type checked.

Branch statements #

break statement #

A for loop or a switch statement can be left prematurely with a break statement. It leaves the innermost construct, unless a label of a construct is given:

for cond {
	switch {
		if cond {
			break // break out of the `switch` statement

	break // break out of the `for` statement

loop: for cond1 {
	for cond2 {
		break loop // leaves both loops

exit: {
    if true {
        break exit // works with labeled blocks too
    fmt.println("This line will never print.")

continue statement #

As in many programming languages, a continue statement starts the next iteration of a loop prematurely:

for cond {
	if get_foo() {

fallthrough statement #

Odin’s switch is like the one in C or C++, except that Odin only runs the selected case. This means that a break statement is not needed at the end of each case. Another important difference is that the case values need not be integers nor constants.

fallthrough can be used to explicitly fall through into the next case block:

switch i {
case 0:
case 1:

Procedures #

In Odin, a procedure is something that can do work, which some languages call functions or methods. A procedure literal in Odin is defined with the proc keyword:

fibonacci :: proc(n: int) -> int {
	switch {
	case n < 1:
		return 0
	case n == 1:
		return 1
	return fibonacci(n-1) + fibonacci(n-2)

fmt.println(fibonacci(3)) // 2

For more information regarding value declarations in general, please see the Odin FAQ.

Parameters #

Procedures can take zero or many parameters. The following example is a basic procedure that multiplies two integers together:

multiply :: proc(x: int, y: int) -> int {
	return x * y
fmt.println(multiply(137, 432))

When two or more consecutive parameters share a type, you can omit the other types from previous names, like with variable declarations. In this example: x: int, y: int can be shortened to x, y: int, for example:

multiply :: proc(x, y: int) -> int {
	return x * y
fmt.println(multiply(137, 432))

Continuing the C family tradition, everything in Odin is passed by value (rather than by reference, e.g. FORTRAN, Java, etc). However, Odin differs from the C/C++ tradition in that all procedure parameters in Odin are immutable values. This allows for numerous optimizations with the Odin calling conventions ("odin" and "contextless") which would not be possible with the original C tradition of always passing a copy of the thing that has been passed.

Passing a pointer value makes a copy of the pointer, not the data it points to. Slices, dynamic arrays, and maps behave like pointers in this case (Internally they are structures that contain values, which include pointers, and the “structure” is passed by value).

To mutate the procedure parameter (like in C), an explicit copy is required. This can be done through shadowing the variable declaration:

foo :: proc(x: int) {
	x := x // explicit mutation
	for x > 0 {
		x -= 1

Procedures can be variadic, taking a varying number of arguments:

sum :: proc(nums: -> (result: int) {
	for n in nums {
		result += n
fmt.println(sum())              // 0
fmt.println(sum(1, 2))          // 3
fmt.println(sum(1, 2, 3, 4, 5)) // 15

odds := []int{1, 3, 5}
fmt.println(sum(..odds))        // 9, passing a slice as varargs

Multiple results #

A procedure in Odin can return any number of results. For example:

swap :: proc(x, y: int) -> (int, int) {
	return y, x
a, b := swap(1, 2)
fmt.println(a, b) // 2 1

Named results #

Return values in Odin may be named. If so, they are treated as variables defined at the top of the procedure, like input parameters. A return statement without arguments returns the named return value. “Naked” return statements should only be used in short procedures as it reduces clarity when reading.

do_math :: proc(input: int) -> (x, y: int) {
	x = 2*input + 1
	y = 3*input / 5
	return x, y
do_math_with_naked_return :: proc(input: int) -> (x, y: int) {
	x = 2*input + 1
	y = 3*input / 5

Named arguments #

When calling a procedure, it is not clear in which order parameters might appear. Therefore, the arguments can be named, like a struct literal, to make it clear which argument a parameter is for:

create_window :: proc(title: string, x, y: int, width, height: int, monitor: ^Monitor) -> (^Window, Window_Error) {...}

window, err := create_window(title="Hellope Title", monitor=nil, width=854, height=480, x=0, y=0)

As of the dev-2023-07 release, mixing named and positional arguments is allowed. This is often useful when a procedure has a lot of arguments or you want to customize default values.

Positional arguments are not allowed after named arguments.

foo :: proc(value: int, name: string, x: bool, y: f32, z := 0) { }
foo(134, "hellope", x=true, y=4.5)

Default values #

The create_window procedure may be easier to use if default values are provided, which will be used if they are not specified:

create_window :: proc(title: string, x := 0, y := 0, width := 854, height := 480, monitor: ^Monitor = nil) -> (^Window, Window_Error) {...}

window1, err1 := create_window("Title1")
window2, err2 := create_window(title="Title1", width=640, height=360)

Note: These default values must be compile time known values, such as a constant value or nil (if the type supports it).

Explicit procedure overloading #

Unlike other languages, Odin provides the ability to explicitly overload procedures:

bool_to_string :: proc(b: bool) -> string {...}
int_to_string  :: proc(i: int)  -> string {...}

to_string :: proc{bool_to_string, int_to_string}

Rationale behind explicit overloading #

The design goals of Odin were explicitness and simplicity. Implicit procedure overloading complicates the scoping system. In C++, you cannot nest procedures within procedures, so all procedure look-ups are done at the global scope. In Odin, procedures can be nested within procedures and, as a result, determining which procedure should be used, in the case of implicit overloading, is complex.

Explicit overloading has many advantages:

  • Explicitness of what is overloaded
  • Able to refer to the specific procedure if needed
  • Clear which scope the entity name belongs to
  • Ability to specialize parametric polymorphic procedures if necessary, which have the same parameter but different bounds (see where clauses)
foo :: proc{

Basic types #

Odin’s basic types are:

bool b8 b16 b32 b64 // booleans

// integers
int  i8 i16 i32 i64 i128
uint u8 u16 u32 u64 u128 uintptr

// endian specific integers
i16le i32le i64le i128le u16le u32le u64le u128le // little endian
i16be i32be i64be i128be u16be u32be u64be u128be // big endian

f16 f32 f64 // floating point numbers

// endian specific floating point numbers
f16le f32le f64le // little endian
f16be f32be f64be // big endian

complex32 complex64 complex128 // complex numbers

quaternion64 quaternion128 quaternion256 // quaternion numbers

rune // signed 32 bit integer
	 // represents a Unicode code point
	 // is a distinct type to `i32`

// strings
string cstring

// raw pointer type

// runtime type information specific type

The uintptr type is pointer sized, and the int, uint types are the “natural” register size, which is guaranteed to greater than or equal to the size of a pointer (i.e. size_of(uint) >= size_of(uintptr)). When you need an integer value, you should default to using int unless you have a specific reason to use a sized or unsigned integer type

Note: The Odin string type stores the pointer to the data and the length of the string. cstring is used to interface with foreign libraries written in/for C that use zero-terminated strings.

Zero values #

Variables declared without an explicit initial value are given their zero value.

The zero value is:

  • 0 for numeric and rune types
  • false for boolean types
  • "" (the empty string) for strings
  • nil for pointer, typeid, and any types.

The expression {} can be used for all types to act as a zero type. This is not recommended as it is not clear and if a type has a specific zero value shown above, please prefer that.

Type conversion #

The expression T(v) converts the value v to the type T.

i: int = 123
f: f64 = f64(i)
u: u32 = u32(f)

or with type inference:

i := 123
f := f64(i)
u := u32(f)

Unlike C, assignments between values of a different type require an explicit conversion.

Cast operator #

The cast operator can also be used to do the same thing:

i := 123
f := cast(f64)i
u := cast(u32)f

This is useful in some contexts but has the same semantic meaning.

Transmute operator #

The transmute operator is a bit cast conversion between two types of the same size:

f := f32(123)
u := transmute(u32)f

This is akin to doing the following pointer cast manipulations:

f := f32(123)
u := (^u32)(&f)^

However, transmute does not require taking the address of the value in question, which may not be possible for many expressions.

Untyped types #

In the Odin type system, certain expressions will have an “untyped” type. An untyped type can implicitly convert to a “typed” type.

I :: 42        // untyped integer, will implicitly convert to any numeric type (int, u32, f64, quaternion128 etc)
F :: 1.37      // untyped float,  will implicitly convert to any numeric type that can support fractional parts (f64, quaternion128 etc)
S :: "Hellope" // untyped string,  will implicitly convert to string and cstring
B :: true      // untyped boolean, will implicitly convert to bool, b8, b16, etc.

Auto cast operation #

The auto_cast operator automatically casts an expression to the destination’s type if possible:

x: f32 = 123
y: int = auto_cast x

Note: This operation is only recommended to be used for prototyping and quick tests. Please do not abuse it.

Built-in constants, values, and procedures #

There are a few built-in constants and values in Odin which have different uses:

false // untyped boolean constant equivalent to the expression 0!=0
true  // untyped boolean constant equivalent to the expression 0==0
nil   // untyped nil value used for certain values
---   // untyped undefined value used to explicitly not initialize a variable

--- is useful if you want to explicitly not initialize a variable with any default value:

x: int // initialized with its zero value
y: int = --- // uses uninitialized memory

This is the default behaviour in C, whilst the default behaviour in Odin is to zero the memory.

Built-in procedures #

For the full list of builtin-procedures, see the documentation for package builtin.

There are two kinds of built-in procedures in Odin:

  • Compiler defined
  • Core library defined

string type #

As previously mentioned the odin string type is just a rawptr + len.

The core:strings library was created to help dealing with string cloning, conversion of string<->cstring and other calls you find in standard libraries.

All procedures are documented and can be easily understood with code examples.

string iteration #

Iterating a string can be done in two ways - by runes or by bytes.

// by runes
x := "ABC"
for codepoint, index in x {
	fmt.println(index, codepoint)
	// 0 A
	// 1 B
	// 2 C

// by bytes - string length is in bytes
for index in 0..<len(x) {
	fmt.println(index, x[index])
	// 0 65
	// 1 66
	// 2 67

Iteration through runes is preferred since odin strings are UTF8. Most core library procedures will be addressed by *_byte if they do input/output an index in byte.

string format printing #

The core:fmt library supports printing strings from byte arrays in structs, when additional tag information is supplied.

Foo :: struct {
	a: [L]u8 `fmt:"s"`, // whole buffer is a string
	b: [N]u8 `fmt:"s,0"`, // 0 terminated string
	c: [M]u8 `fmt:"q,n"`, // string with length determined by n, and use %q rather than %s
	n: int `fmt:"-"`, // ignore this from formatting

cstring type #

The cstring type is a c-style string value, which is zero-terminated. It is equivalent to char const * in C. Its primary purpose is for easy interfacing with C. Please see the foreign system for more information.

A cstring is easily convertible to an Odin string. However, to convert a string to a cstring, it requires allocations if the value is not constant.

str:  string  = "Hellope"
cstr: cstring = "Hellope" // constant literal
cstr2 := string(cstr)     // O(n) conversion as it requires search from the zero-terminator
nstr  := len(str)  // O(1)
ncstr := len(cstr) // O(n)

string type conversions #

Here is a short list of possible type conversions - including whether they copy or alias. This is important to understand since Odin gives you the possibility to keep allocations to a low degree.

If some cases are missing please let us know.


  • copy = get a freshly allocated copy of the ‘from’ data
  • alias = reuse the ‘from’ data, without allocation
  • stream = get individual values from the string, without allocation
  • st = the input string

From string to X #

To Action Code
[]u8 alias transmute([]u8)st
string copy strings.clone(st)
cstring copy strings.clone_to_cstring(st)
cstring alias strings.unsafe_string_to_cstring(st)
[]rune stream for rune in st { ... }
[]rune copy utf8.string_to_runes(st)
[^]u8 alias raw_data(st)

From cstring to X #

To Action Code
string alias string(st)
[^]u8 alias transmute([^]u8)st

From a string literal to X #

To Action Code
string alias string(st) or newstr: string = st
cstring alias cstring(st) or newstr: cstring = st

From []u8 to X #

To Action Code
string alias transmute(string)st
string alias string(st) unless a slice literal
[^]u8 alias raw_data(st)

From []rune to string #

Action Code
copy utf8.runes_to_string(st)

From [^]u8 to cstring #

Action Code
alias cstring(st)

From [^]u8 and length int to string #

Action Code
alias strings.string_from_ptr(ptr, length)

Operators #

Operators combine operands into expressions. For binary operations, operand types must be identical or implicitly convertible unless the operation involves shifts or untyped constants.

Arithmetic operators #


+                           is 0 + x
-    negation               is 0 - x
~    bitwise complement     is m ~ x where m = "all bits set to 1" for unsigned x
                                     and m = -1 for signed x


+       sum                        integers, enums, floats, complex values, quaternions, arrays of numeric types, matrices, constant strings
-       subtraction                integers, enums, floats, complex values, quaternions, arrays of numeric types, matrices
*       multiplication             integers, floats, complex values, quaternions, arrays of numeric types, matrices
/       division                   integers, floats, complex values, quaternions, arrays of numeric types
%       modulo (truncated)         integers
%%      remainder (floored)        integers

|       bitwise or                 integers, enums
~       bitwise xor                integers, enums
&       bitwise and                integers, enums
&~      bitwise and-not            integers, enums
<<      left shift                 integer << integer >= 0
>>      right shift                integer >> integer >= 0

Except for shift operations, if one operand is an untyped constant and the other operand is not, the constant is implicitly converted to the type of the other operand (if possible).

The right operand in a shift expression must have an unsigned integer type or be an untyped constant representable by a typed unsigned integer. If the left operand of a non-constant shift expression is an untyped constant, it is first implicitly converted to the type it would assume if the shift expression were replaced solely by the left operand alone (with type inference and hinting rules applied).

Comparison operators #

==      equal
!=      not equal
<       less
<=      less or equal
>       greater
>=      greater or equal
&&      short-circuiting logical and
||      short-circuiting logical or

In any comparison, the first operand must be assignable to the type of the second, or vice versa.

The equality operators == and != apply to operands that are comparable. The ordering operators <, <=, >, and >= apply to operands that are ordered. These terms and the result of the comparisons are defined as follows:

  • Boolean values are comparable.
  • Integers values are comparable and ordered.
  • Floating-point values are comparable and ordered, defined by the IEEE-754 standard.
  • Complex values are comparable.
  • Quaternion values are comparable.
  • Rune values are comparable and ordered.
  • String values are comparable and ordered, lexically byte-wise.
  • Matrix values are comparable.
  • Pointer values are comparable and ordered.
  • Multi-pointer values are comparable and ordered.
  • Soa-pointer values are comparable.
  • Enum values are comparable and ordered.
  • Bit-set values are comparable.
  • Struct values are comparable if all their fields are comparable.
  • Union values are comparable if all their variants are comparable.
  • Array and enumerated array values are comparable if values of the element type are comparable.
  • typeid is comparable.
  • Simd vectors are comparable.

Bit-set values use different logic compared to integers when comparison operators are used: please see the section of bit sets

Logical operators #

Logical operators apply to boolean values. The right operand is evaluated conditionally

&&      conditional AND    a && b  is "b if a else false"
||      conditional OR     a || b  is "true if a else b"
!       NOT                !a      is "not a"

Compound binary operator and assign #

Like many other languages, there is a shorthand for performing a binary operation and assigning the result to the first operand e.g. x = x + 5. All arithmetic and logical binary operators have this shorthand

+=       sum and assign                   a += b is a = a + b
-=       subtraction and assign           a -= b is a = a - b
*=       multiplication and assign        a *= b is a = a * b
/=       division and assign              a /= b is a = a / b
%=       modulo (truncated) and assign    a %= b is a = a % b
%%=      remainder (floored) and assign   a %%= b is a = a %% b

|=       bitwise or and assign            a |= b is a = a | b
~=       bitwise xor and assign           a ~= b is a = a ~ b
&=       bitwise and and assign           a &= b is a = a & b
&~=      bitwise and-not and assign       a &~= b is a = a &~ b
<<=      left shift and assign            a <<= b is a = a << b
>>=      right shift and assign           a >>= b is a = a >> b

&&=      conditional AND and assign       a &&= b is a = a && b
||=      conditional OR and assign        a ||= b is a = a || b

Address operator #

For an operand x of type T, the address operation &x generates a pointer of ^T to x. The operand must be addressable, meaning that either a variable, pointer indirection, or slice/dynamic array indexing operator; or a field selector of an addressable struct operand; or an array index operation of an addressable array; or a type assertion of an addressable union or any; or a compound literal value.

For an operand x of pointer type ^T, the pointer indirection x^ denotes the variable of type T pointed to by x. If x is an invalid address, such as nil, an attempt to evaluate x^ will result in platform specific behaviour - on most platforms this will be a segmentation fault.

&Foo{1, 2}


x: ^int = nil
x^      // causes a runtime panic

Ternary Operators #

x if cond else y    // ternary runtime conditional expression
x when cond else y  // ternary compile-time conditional expression
cond ? x : y        // ternary runtime conditional expression, equivalent to "x if cond else y"

Other operators #

  • or_else
  • or_return
  • or_continue
  • or_break
  • in - set membership (e in A, A contains element e)
    • Used for bit_set types and map types
  • not_in - not set membership (e not_in A, A does not contain e)
    • Used for bit_set types and map types
  • ..= - inclusive range
  • ..< - half open range

The range operations ..= and ..< are only possible within certain contexts:

for x in a..<b {}
for x in a..=b {}

switch x {
case a..<b:
case c..=d:


in and not_in are not allowed in within a for loop condition without ambiguity:

for x in y {}    // range loop
for (x in y) {}  // condition-only for-loop (while-loop in some other languages)

Operator precedence #

Unary operators have the highest precedence.

There are seven precedence levels for binary (and ternary) operators.

Precedence    Operator
     7           *   /   %   %%   &   &~  <<   >>
     6           +   -   |   ~    in  not_in
     5           ==  !=  <   >    <=  >=
     4           &&
     3           ||
     2           ..=    ..<
     1           or_else     ?    if  when

Binary operators of the same precedence associate from left to right. For instance x / y * z is the same as (x / y) * z.

Integer operators #

For two integers values x and y, the integer quotient q = x/y and remainder r = x%y satisfies the following relationships:

x = q*y + r   and |r| < |y|

with x/y truncated towards zero (truncated division).

For two integers values x and y, the integer quotient q = x/y and remainder r = x%%y satisfies the following relationships:

r = x - y*floor(x/y)

The exception to these rules are when the dividend x is the most non-negative value for the integer type of x, and the quotient q = x/-1 is equal to x (and r or m = 0) due to two’s complement integer overflow.

If the divisor is a constant, it must not be zero. If the divisor is zero at runtime, a runtime panic occurs.

The shift operators shift the left operand by the shift count specified by the right operand, which must be non-negative. The shift operators implement arithmetic shifts if the left operand is a signed integer and logical shifts if the left operand is an unsigned integer. There is not an upper limit on the shift count. Shifts behave as if the left operand is shifted n times by 1 for a shift count of n. Therefore, x<<1 is the same as x*2 and x>>1 is the same as x/2 but truncated towards negative infinity.

// These are equivalent:
x << y
x << y if y < 8*size_of(x) else 0

x >> y
x >> y if y < 8*size_of(x) else 0

Integer overflow #

For unsigned integers, the operations +, -, *, and << are computed modulo 2n, where n is the bit width of the unsigned integer’s type. In a sense, these unsigned integer operations discard the high bits upon overflow, and programs may rely on “wrap around”.

For signed integers, the operations +, -, *, /, and << may legally overflow and the resulting value exists and is deterministically defined by the signed integer representation. Overflow does not cause a runtime panic. A compiler may not optimize code under the assumption that overflow does not occur. For instance, x < x+1 may not be assumed to be always true.

Floating-point operators #

For floating-point, complex numbers, quaternions, and other floating-point embedded types:

  • +x is the same as x
  • -x is the negation of x

The result of a floating-point related division by zero is not specified beyond the IEEE-754 standard; a runtime panic will occur.

An implementation may combine multiple floating-point operations into a single fused operation, and produce a result that differs from the value obtained by executing and rounding the instructions individually.

Advanced types #

Type alias #

You can alias a named type with another name:

My_Int :: int
#assert(My_Int == int)

Distinct types #

A distinct type allows for the creation of a new type with the same underlying semantics.

My_Int :: distinct int
#assert(My_Int != int)

Aggregate types (struct, enum, union) will always be distinct even when named.

Foo :: struct {}
#assert(Foo != struct{})

Fixed arrays #

An array is a simplified fixed length container. Each element in an array has the same type. An array’s index can be any integer, character, or enumeration type.

An array can be constructed like the following:

x := [5]int{1, 2, 3, 4, 5}
for i in 0..=4 {

The notation x[i] is used to access the i-th element of x; and 0-index based (like C).

The above array can also be constructed with a question mark (?) to automatically infer its length:

x := [?]int{1, 2, 3, 4, 5}

The built-in len proc returns the array’s length.

x: [5]int
#assert(len(x) == 5)

Array access is bounds checked by default, both at compile-time (with constant indices) and at runtime. This can be disabled and enabled at a per block level with the #no_bounds_check and #bounds_check directives, respectively:

#no_bounds_check {
	x[n] = 123 // n could be in or out of range of valid indices

#no_bounds_check can be used to improve performance when the bounds are known to not exceed.

Array programming #

Odin’s fixed length arrays support array programming.


Vector3 :: [3]f32
a := Vector3{1, 4, 9}
b := Vector3{2, 4, 8}
c := a + b  // {3, 8, 17}
d := a * b  // {2, 16, 72}
e := c != d // true

n.b. Odin also supports matrix types.

Swizzle Operations #
a := [3]f32{10, 20, 30}
b := swizzle(a, 2, 1, 0)
assert(b == [3]f32{30, 20, 10})

c := swizzle(a, 0, 0)
assert(c == [2]f32{10, 10})
assert(c == 10) // assert all elements == 10

Builtin implicit swizzle fields are available on any array with length <= 4 as xyzw and rgba.

Vector3 :: distinct [3]f32
a := Vector3{1, 2, 3}
b := Vector3{5, 6, 7}
c := (a * b)/2 + 1
d := c.x + c.y + c.z
fmt.printf("%.1f\n", d) // 22.0

cross :: proc(a, b: Vector3) -> Vector3 {
	i := swizzle(a, 1, 2, 0) * swizzle(b, 2, 0, 1)
	j := swizzle(a, 2, 0, 1) * swizzle(b, 1, 2, 0)
	return i - j

cross_shorter :: proc(a, b: Vector3) -> Vector3 {
	i := a.yzx * b.zxy
	j := a.zxy * b.yzx
	return i - j

blah :: proc(a: Vector3) -> f32 {
	return a.x + a.y + a.z

x := cross(a, b)

Slices #

Slices look similar to arrays however, their length is not known at compile time. The type []T is a slice with elements of type T. In practice, slices are much more common than arrays.

A slice is formed by specifying two indices, a low and high bound, separated by a colon:

a[low : high]

This selects a half-open range which includes the lower element, but excludes the higher element.

fibonaccis := [6]int{0, 1, 1, 2, 3, 5}
s: []int = fibonaccis[1:4] // creates a slice which includes elements 1 through 3
fmt.println(s) // 1, 1, 2

Slices are like references to arrays; they do not store any data, rather they describe a section, or slice, of underlying data.

Internally, a slice stores a pointer to the data and an integer to store the length of the slice.

The built-in len proc returns the array’s length.

x: []int = ...
length_of_x := len(x)

Slice literals #

A slice literal is like an array literal without the length. This is an array literal:

[3]int{1, 6, 3}

This is a slice literal which creates the same array as above, and then creates a slice that references it:

[]int{1, 6, 3}

Slice shorthand #

For the array:

a: [6]int

these slice expressions are equivalent:


When grabbing a chunk of a slice:


can also be written:


Nil slices #

The zero value of a slice is nil. A nil slice has a length of 0 and does not point to any underlying memory. Slices can be compared against nil and nothing else.

s: []int
if s == nil {
	fmt.println("s is nil!")

Sort slices #

A slice literal can be sorted in ascending order as follows:

s := []int{1, 6, 3, 5 ,7, 3, 0}

or in descending order

r := []int{1, 6, 3, 5 ,7, 3, 0}

Dynamic arrays #

Dynamic arrays are similar to slices, but their lengths may change during runtime. Dynamic arrays are resizeable and they are allocated using the current context’s allocator.

x: [dynamic]int

Along with the built-in proc len, dynamic arrays also have cap which can used to determine the dynamic array’s current underlying capacity.

Appending to a dynamic array #

It is common to append new elements to a dynamic array; this can be done using the built-in append proc.

x: [dynamic]int
append(&x, 123)
append(&x, 4, 1, 74, 3) // append multiple values at once

y: [dynamic]int
append(&y, ..x[:]) // append a slice

Inject / Assign to a dynamic array #

Injecting into a specific index can be done with inject. It will move other elements upwards when inserted below other elements.

Assign a type at a specific index can be done with assign. It’s the same as doing x[index] = 10.

Both of these procedures will resize the dynamic array len to the wanted index. This can be seen in the example below.

x := make([dynamic]int, 0, 16)
inject_at(&x, 0, 10)
inject_at(&x, 3, 10) // resizes till length
fmt.eprintln(x[:], len(x), cap(x)) // [10, 0, 0, 10] 4 16
assign_at(&x, 3, 20)
assign_at(&x, 4, 30)
fmt.eprintln(x[:], len(x), cap(x)) // [10, 0, 0, 20, 30] 5, 16
assign_at(&x, 5, 40, 50, 60)
fmt.eprintln(x[:], len(x), cap(x)) // [10, 0, 0, 20, 30, 40, 50, 60] 8 16

Removing from a dynamic array #

Removing from a dynamic array can be done in several ways using the built-in procedures:

  • pop pops the last element of the array
  • unordered_remove removes an element at a specific index. Unordered means it is O(1), since it swaps the last element to the removed location - making the array be sorted differently.
  • ordered_remove removes an element at a specific index. Ordered means it will move all elements after the index downwards with a copy - ensuring elements remain in the same order.
x: [dynamic]int
append(&x, 1, 2, 3, 4, 5) // [1, 2, 3, 4, 5]
pop(&x) // [1, 2, 3, 4]
ordered_remove(&x, 0) // [2, 3, 4]
unordered_remove(&x, 0) // [4, 3]

Other variants can be found in the built-in procedures documentation.

Slice & Sort a dynamic array #

Although dynamic arrays and slices are different concepts, dynamic arrays can be ‘sliced’ and sorted as follows:

s: [dynamic]int
append(&s, 1, 6, 3, 5, 7, 3, 0) // [1, 6, 3, 5, 7, 3, 0]
slice.sort(s[:]) // [0, 1, 3, 3, 5, 6, 7]

Making and deleting slices and dynamic arrays #

Slices and dynamic arrays can be explicitly allocated with the built-in make proc.

a := make([]int, 6)           // len(a) == 6
b := make([dynamic]int, 6)    // len(b) == 6, cap(b) == 6
c := make([dynamic]int, 0, 6) // len(c) == 0, cap(c) == 6
d := []int{1, 2, 3}           // a slice literal, for comparison

// with an explicit allocator:
e := make([]int, 6, context.allocator)
f := make([dynamic]int, 0, 6, context.allocator)

Slices and dynamic arrays can be deleted with the built-in delete proc.

// delete(d)                  // no need to clean up slice literals
delete(e)                     // slices are always deleted from context.allocator
delete(f)                     // dynamic arrays remember their allocator

Note: There is no automatic memory management in Odin.

Clearing a dynamic array #

Instead of deleting the array you often want to simply clear the dynamic array. This will set the length len() to be 0, while the capacity cap remains the same.

x: [dynamic]int
append(&x, 1, 2, 3, 4, 5) // [1, 2, 3, 4, 5]
fmt.println(len(x)) // 5
clear(&x) // []
fmt.println(len(x)) // 0

Resize / Reserve with a dynamic array #

Often enough we also want to resize or reserve a specific amount for a dynamic array. It’s important to understand the difference between the two operations.

  • resize will try to resize memory of a passed dynamic array to the requested element count (setting the len, and possibly cap).
  • reserve will try to reserve memory of a passed dynamic array to the requested element count (setting the cap).
  • shrink will shrink the capacity of a dynamic array down to the current length, or the given capacity.
x: [dynamic]int
fmt.println(len(x), cap(x)) // 0 0
append(&x, 1, 2, 3) // [1, 2, 3]
fmt.println(len(x), cap(x)) // 3 8
resize(&x, 5) 
fmt.println(x[:]) // [1, 2, 3, 0, 0] other values are zero'd memory
fmt.println(len(x), cap(x)) // 5 8
reserve(&x, 32)
fmt.println(len(x), cap(x)) // 5 32
fmt.println(len(x), cap(x)) // 5 5

Small_Array(N, T) container dynamic array #

The core library also contains a container dynamic array Small_Array(N, T). It implements most dynamic array procedures while being able to remain on the stack.

Short Example:

import sa "core:container/small_array"

x: sa.Small_Array(8, int)
fmt.println(sa.len(x), sa.cap(x)) // 0 8
sa.append(&x, 1, 2, 3) 
fmt.println(sa.len(x), sa.cap(x)) // 3 8
fmt.println(sa.slice(&x)) // [1, 2, 3]

Enumerations #

Enumeration types define a new type whose values consist of the ones specified. The values are ordered, for example:

Direction :: enum{North, East, South, West}

The following holds:

int(Direction.North) == 0
int(Direction.East)  == 1
int(Direction.South) == 2
int(Direction.West)  == 3

Enum fields can be assigned an explicit value:

Foo :: enum {
	B = 4, // Holes are valid
	C = 7,
	D = 1337,

If an enumeration requires a specific size, a backing integer type can be specified. By default, int is used as the backing type for an enumeration.

Foo :: enum u8 {A, B, C} // Foo will only be 8 bits

Implicit Selector Expression #

An implicit selector expression is an abbreviated way to access a member of an enumeration, in a context where type inference can determine the implied type. It has the following form:


For example:

Foo :: enum{A, B, C}
f: Foo
f = Foo.A
f = .A

switch f {
case .A:
case .B:
case .C:

using can also be used with an enumeration to bring the fields into the current scope:

main :: proc() {
	Foo :: enum {A, B, C}
	using Foo
	a := A


Note: Implicit selector expression is preferred to using an enumeration as using does pollute the current scope.

Iterating an Enumeration #

Enums can be trivially for looped in odin. This way we can loop through the entire enum and do things like printing or inserting into an Enumerated Array.

Direction :: enum{North, East, South, West}

for direction, index in Direction {
	fmt.println(index, direction) 
	// 0 North
	// 1 East
	// 2 South
	// 3 West

Enumerated Array #

Enumerated Arrays allow the use of an Enum to be used as indices to a fixed array.

We’ll extend the Direction enum used previously to add direction vectors.

Direction :: enum{North, East, South, West}

Direction_Vectors :: [Direction][2]int {
	.North = {  0, -1 },
	.East = { +1,  0 },
	.South = {  0, +1 },
	.West = { -1,  0 },

assert(Direction_Vectors[.North] == { 0, -1 })
assert(Direction_Vectors[.East] == { 1, 0 })
assert(Direction_Vectors[cast(Direction) 2] == { 0, 1 })

The #partial directive can be used to initialize an enumerated array partially.

arr: [enum {A, B, C}]int
arr = #partial { // without partial the compiler would complain
	.A = 42,
fmt.println(arr) // [.A = 42, .B = 0, .C = 0]

Bit sets #

The bit_set type models the mathematical notion of a set. A bit_set’s element type can be either an enumeration or a range:

Direction :: enum{North, East, South, West}

Direction_Set :: bit_set[Direction]

Char_Set :: bit_set['A'..='Z']

Number_Set :: bit_set[0..<10] // bit_set[0..=9]

Bit sets are implemented as bit vectors internally for high performance. The zero value of a bit set is either nil or {}.

x: Char_Set
x = {'A', 'B', 'Y'}
y: Direction_Set
y = {.North, .West}

Bit sets support the following operations:

  • A + B - union of two sets (equivalent to A | B)
  • A - B - difference of two sets (A without B’s elements) (equivalent to A &~ B)
  • A & B - intersection of two sets
  • A | B - union of two sets (equivalent to A + B)
  • A &~ B - difference of two sets (A without B’s elements) (equivalent to A - B)
  • A ~ B - symmetric difference (Elements that are in A and B but not both)
  • A == B - set equality
  • A != B - set inequality
  • A <= B - subset relation (A is a subset of B or equal to B)
  • A < B - strict subset relation (A is a proper subset of B)
  • A >= B - superset relation (A is a superset of B or equal to B)
  • A > B - strict superset relation (A is a proper superset of B)
  • e in A - set membership (A contains element e)
  • e not_in A - A does not contain element e

Bit sets are often used to denote flags. This is much cleaner than defining integer constants that need to be bitwise or-ed together.

If a bit set requires a specific size, the underlying integer type can be specified:

Char_Set :: bit_set['A'..='Z'; u64]
#assert(size_of(Char_Set) == size_of(u64))

To get the number of elements set, its cardinality, of a bit_set, use the built-in card procedure:

x: Direction_Set
x = {.North, .West}
count := card(x)
assert(count == 2)

Pointers #

Odin has pointers. A pointer is a memory address of a value. The type ^T is a pointer to a T value. Its zero value is nil.

p: ^int

The & operator takes the address of its operand (if possible):

i := 123
p := &i

The ^ operator dereferences the pointer’s underlying value:

fmt.println(p^) // read `i` through the pointer `p`
p^ = 1337       // write `i` through the pointer `p`

Note: C programmers may be used to using * to denote pointers. In Odin, the ^ syntax is borrowed from Pascal. This is to keep the convention of the type on the left and its usage on the right:

p: ^int // ^ on the left
x := p^ // ^ on the right

Note: Unlike C, Odin has no pointer arithmetic. If you need a form of pointer arithmetic, please use the ptr_offset and ptr_sub procedures in the "core:mem" package.

Structs #

A struct is a record type in Odin. It is a collection of fields. Struct fields are accessed by using a dot:

Vector2 :: struct {
	x: f32,
	y: f32,
v := Vector2{1, 2}
v.x = 4

Struct fields can be accessed through a struct pointer:

v := Vector2{1, 2}
p := &v
p.x = 1335

We could write p^.x, however, it is nice to not have to explicitly dereference the pointer. This is very useful when refactoring code to use a pointer rather than a value, and vice versa.

Struct literals #

A struct literal can be denoted by providing the struct’s type followed by {}. A struct literal must either provide all the arguments or none:

Vector3 :: struct {
	x, y, z: f32,
v: Vector3
v = Vector3{} // Zero value
v = Vector3{1, 4, 9}

You can list just a subset of the fields if you specify the field by name (the order of the named fields does not matter):

v := Vector3{z=1, y=2}
assert(v.x == 0)
assert(v.y == 2)
assert(v.z == 1)

Structs can be nested by defining a field as a struct.

Foo :: struct {
	a, b, c: int,
	bar_1: struct {
		x, y, z: int,

	bar_2: struct {
		x, y, z: int,

	_: struct {
		x, y, z: int,

Struct directives #

Structs can be annotated with different memory layout and alignment requirements:

struct #align(4) {...} // align to 4 bytes
struct #packed {...} // remove padding between fields
struct #raw_union {...} // all fields share the same offset (0). This is the same as C's union

Struct field tags #

Struct fields can be tagged with a string literal to attach meta-infomration which can be used with runtime-type information. Usually this is used to provide transactional information info on how a struct field is encoded to or decoded from another format, but you can store whatever you want within the string literal

User :: struct {
	flag: bool, // untagged field
	age:  int    "custom whatever information",
	name: string `json:"username" xml:"user-name" fmt:"q"`, // `core:reflect` layout

Within Odin’s core library, the standard convention is to store a key that denotes the package and then a subsequence "value". For example, json keys are processed and used by core:encoding/json package, fmt keys are processed by core:fmt.

If multiple information is to be passed in the "value", usually it is specified by separating it with a common (,), e.g.

name: string `json:"username,omitempty",

n.b. Field tags also exist for bit_field record types.

Unions #

A union in Odin is a discriminated union, also known as a tagged union or sum type. The zero value of a union is nil.

Value :: union {
v: Value
v = "Hellope"

// type assert that `v` is a `string` and panic otherwise
s1 := v.(string)

// type assert but with an explicit boolean check. This will not panic
s2, ok := v.(string)

Type switch statement #

A type switch is a construct that allows several type assertions in series. A type switch is like a regular switch statement, but the cases are types (not values). For a union, the only case types allowed are that of the union.

value: Value = ...
switch v in value {
case string:
	#assert(type_of(v) == string)

case bool:
	#assert(type_of(v) == bool)

case i32, f32:
	// This case allows for multiple types, therefore we cannot know which type to use
	// `v` remains the original union value
	#assert(type_of(v) == Value)
	// Default case
	// In this case, it is `nil`

Union tags #

Applying the #no_nil tag to a union type states it does not have a nil value. Unions with #no_nil must have at least two variants and the first variant is its default type:

Value :: union #no_nil {bool, string}
v: Value
_, ok := v.(bool)

The #shared_nil tag normalizes each variant’s nil value into nil on assigment. If you assign nil or zero values to a union with #shared_nil the union will be nil. Unions with #shared_nil require all variants to have a nil value.

Error :: union #shared_nil {

File_Error :: enum {
	None = 0,

Memory_Error :: enum {
	None = 0,

shared_nil_example :: proc() {
	an_error: Error
	an_error = File_Error.None

	assert(an_error == nil)

Unions also have the #align tag, like structures:

union #align(4) {...} // align to 4 bytes

Maps #

A map maps keys to values. The zero value of a map is nil. A nil map has no keys. The built-in make proc returns an initialized map using the current context, and delete can be used to delete a map.

m := make(map[string]int)
defer delete(m)
m["Bob"] = 2

To insert or update an element of a map:

m[key] = elem

To retrieve an element:

elem = m[key]

To remove an element:

delete_key(&m, key)

If an element of a key does not exist, the zero value of the element will be returned. Checking to see if an element exists can be done in two ways:

elem, ok := m[key] // `ok` is true if the element for that key exists


ok := key in m // `ok` is true if the element for that key exists

The first approach is called the “comma ok idiom”.

You can also initialize maps with map literals:

m := map[string]int{
	"Bob" = 2,
	"Chloe" = 5,

Modifying existing map slots needs to be done in two steps. However assigning to a struct field is prohibited.

Test :: struct {
	x: int,
	y: int,

m := map[string]Test{
	"Bob" = { 0, 0 },
	"Chloe" = { 1, 1 },

value, ok := &m["Bob"]
if ok {
	value^ = { 2, 2 }

fmt.println(m["Bob"]) // { 2, 2 }
m["Bob"] = { 3, 3 }
fmt.println(m["Bob"]) // { 3, 3 }
m["Chloe"].x = 0 // PROHIBITED

Map Container Calls #

The built-in map also supports all the standard container calls that can be found with the dynamic array.


  • len(some_map) returns the amount of slots used up
  • cap(some_map) returns the capacity of the map - the map will reallocate when exceeded
  • clear(&some_map) clears the entire map - dynamically allocated content needs to be freed manually
  • reserve(&some_map, capacity) reserves the requested element count
  • shrink(&some_map) shrink the capacity down to the current length

Bit Fields #

A bit_field is a record type in Odin that is akin to a bit-packed struct. Note: bit_field is not equivalent to bit_set as it has different semantics and use cases. bit_field fields are accessed by using a dot:

Foo :: bit_field u16 { // backing type must be an integer or array of integers
    x: i32     | 3, // signed integers will be signed extended on use
    y: u16     | 2 + 3, // general expressions
    z: My_Enum | foo.SOME_CONSTANT, // ability to define the bit-width elsewhere
    w: bool    | foo.SOME_CONSTANT > 10 ? 2 : 1,

v := Foo{}
v.x = 4 // truncates the value to fit into 3 bits
fmt.println(v.x) // accessing will convert `v.x` to an `i32` and do an appropriate sign extension

A bit_field is different from a struct in that you must specify the backing type. This backing type must be an integer or a fixed-length array of integers. This is useful if there needs to be a specific alignment or access pattern for the record.

Foo :: bit_field u32 {...}
Foo :: bit_field [4]u8 {...}


  • If all of the fields in a bit_field are 1-bit in size and are a boolean, please considering using a bit_set instead.
  • Odin’s bit_field and C’s bit-fields might not be compatible
    • Odin’s bit_fields have a well defined layout (Least-Significant-Bit)
    • C’s bit fields on structs are undefined and are not portable across targets and compilers

Procedure type #

A procedure type is internally a pointer to a procedure in memory. nil is the zero value a procedure type.


proc(x: int) -> bool
proc(c: proc(x: int) -> bool) -> (i32, f32)

Or you can assign them to a variable:

Callback :: proc() -> int 
a: Callback // nil 
assert(a == nil)
a = proc() -> int { return 0 }
fmt.println(a()) // 0
a = proc() -> int { return 100 }
fmt.println(a()) // 100

Calling conventions #

Odin supports the following calling conventions:

  • odin - default convention used for an Odin proc. It is the same as cdecl but passes an implicit context pointer on each call. (Note: This is subject to change)
  • contextless - This is the same as odin but without the implicit context pointer.
  • stdcall or std – This is the stdcall convention as specified by Microsoft.
  • cdecl or c – This is the default calling convention generated of a procedure in C.
  • fastcall or fast - This is a compiler dependent calling convention.
  • none - This is a compiler dependent calling convention which will do nothing to parameters.

Most calling conventions exist only to interface with foreign Windows code.

The default calling convention is odin, unless it is within a foreign block, where it is then cdecl.

A procedure type with a different calling convention can be declared like the following:

proc "c" (n: i32, data: rawptr)
proc "contextless" (s: []int)

Procedure types are only compatible with the procedures that have the same calling convention and parameter types.

When binding to C libraries you’ll often end up using proc "c" and also set the current context. For this you’ll need to explicity set the context.

‘typeid’ type #

A typeid is a unique identifier for an Odin type. This construct is used by the any type to denote what the underlying data’s type is.

a := typeid_of(bool)
i: int = 123
b := typeid_of(type_of(i))

A typeid can be mapped to relevant type information which can be used in applications such as printing types and editing data:

import "base:runtime"

main :: proc() {
	u := u8(123)
	id := typeid_of(type_of(u))
	info: ^runtime.Type_Info
	info = type_info_of(id)

‘any’ Type #

An any type can reference any data type. Internally it contains a pointer to the underlying data and its relevant typeid. This is a very useful construct in order to have a runtime type safe printing procedure.

Note: The any value is only valid for as long as the underlying data is still valid. Passing a literal to an any will allocate the literal in the current stack frame.

Note: It is highly recommended that you do not use this unless you know what you are doing. Its primary use is for printing procedures.

Multi Pointers #

Multi-Pointers in Odin are a way to describe foreign (C-like) pointers which act like arrays (pointers that map to multiple items). The type [^]T is a multi-pointer to T value(s). Its zero value is nil.

p: [^]int

What multi-pointers support:

  • Index (without any bounds checking)
  • Slicing (bounds checking on if both the low and high operands are given)
  • Implicit conversions between ^T and [^]T
  • Implicit conversion to rawptr (like all pointers)

What multi-pointers DO NOT SUPPORT:

  • Dereferencing (which makes it closer to a slim-slice than a pointer)

The main purpose of this type is to aid with foreign code and act as a way to auto-document functionality and allow for easier transition to Odin code, especially converting pointers into slices.

The following are the rules for indexing and slicing for multi-pointers, and what type they produce depending on the operands given:

x: [^]T = ...

x[i]   -> T
x[:]   -> [^]T
x[i:]  -> [^]T
x[:n]  -> []T
x[i:n] -> []T

Interacting with Multi-Pointers is easiest using the builtin raw_data() call which can return a Multi-Pointer.

a: [^]int
fmt.println(a) // <nil>
b := [?]int { 10, 20, 30 }
a = raw_data(b[:]) 
fmt.println(a, a[1], b) // 0x7FFCBE9FE688 20 [10, 20, 30]

Note: The name of multi-pointers may be subject to change.

SOA Data Types #

Array of Structures (AoS), Structure of Arrays (SoA), and Array of Structures of Arrays (AoSoA) refer to differing ways to arrange a sequence of data records in memory, with regard to interleaving. These are of interest in SIMD and SIMT programming.

SOA Struct Arrays #

Vector3 :: struct {x, y, z: f32}

N :: 2
v_aos: [N]Vector3
v_aos[0].x = 1
v_aos[0].y = 4
v_aos[0].z = 9


v_aos[1] = {0, 3, 4}
v_aos[1].x = 2

v_soa: #soa[N]Vector3

v_soa[0].x = 1
v_soa[0].y = 4
v_soa[0].z = 9

// Same syntax as AOS and treat as if it was an array
v_soa[1] = {0, 3, 4}
v_soa[1].x = 2

// Can use SOA syntax if necessary
v_soa.x[0] = 1
v_soa.y[0] = 4
v_soa.z[0] = 9

// Same pointer addresses with both syntaxes
assert(&v_soa[0].x == &v_soa.x[0])

// Same fmt printing

Works with arrays of length <= 4 which have the implicit fields xyzw/rgba

Vector3 :: distinct [3]f32

N :: 2
v_aos: [N]Vector3
v_aos[0].x = 1
v_aos[0].y = 4
v_aos[0].z = 9

v_soa: #soa[N]Vector3

v_soa[0].x = 1
v_soa[0].y = 4
v_soa[0].z = 9

SOA Struct Slices and Dynamic Arrays #

Fixed-length SOA types can be sliced to produce SOA slices.

Vector3 :: struct {x: i8, y: i16, z: f32}

N :: 3
v: #soa[N]Vector3
v[0].x = 1
v[0].y = 4
v[0].z = 9

s: #soa[]Vector3
s = v[:]
assert(len(s) == N)

a := s[1:2]
assert(len(a) == 1)

To be complete with SOA slices, Odin also supports SOA dynamic arrays.

d: #soa[dynamic]Vector3

append_soa(&d, Vector3{1, 2, 3}, Vector3{4, 5, 9}, Vector3{-4, -4, 3})

soa_zip and soa_unzip #

SOA is not just useful for high performance scenarios but also for everyday tasks which are normally only achieveable in higher level languages. soa_zip is a built-in procedure which allows the user to treat multiple slices as if they are part of the same data structures, utilizing the power of SOA.

x := []i32{1, 3, 9}
y := []f32{2, 4, 16}
z := []b32{true, false, true}

// produce an #soa slice with the normal slices passed
s := soa_zip(a=x, b=y, c=z)

// iterate over the #soa slice
for v, i in s {
	fmt.println(v, i) // exactly the same as s[i]
	// NOTE: `v` is NOT a temporary value but has a specialized addressing mode
	// which means that when accessing v.a etc, it does the correct transformation
	// internally:
	//         s[i].a === s.a[i]
	fmt.println(v.a, v.b, v.c)

soa_unzip is a built-in procedure which allows the user to recover the slices from an #soa slice.

// Recover the slices from the #soa slice
a, b, c := soa_unzip(s)
fmt.println(a, b, c)

matrix type #

A matrix is a mathematical type built into Odin. It is a regular array of numbers, arranged in rows and columns.

The following represents a matrix that has 2 rows and 3 columns:

m: matrix[2, 3]f32

m = matrix[2, 3]f32{
	1, 9, -13,
	20, 5, -6,

Element types of integers, float, and complex numbers are supported by matrices. There is no support for booleans, quaternions, or any compound type.

Indexing a matrix can be used with the matrix indexing syntax. This mirrors other type usages: type on the left, usage on the right.

elem := m[1, 2] // row 1, column 2

Scalars act as if they are scaled identity matrices and can be assigned to matrices as them

b := matrix[2, 2]f32{}
f := f32(3)
b = f

fmt.println("b", b)
fmt.println("b == f", b == f)

Matrices support multiplication between matrices:

a := matrix[2, 3]f32{
	2, 3, 1,
	4, 5, 0,

b := matrix[3, 2]f32{
	1, 2,
	3, 4,
	5, 6,

fmt.println("a", a)
fmt.println("b", b)

c := a * b
#assert(type_of(c) == matrix[2, 2]f32)
fmt.tprintln("c = a * b", c)		

Matrices support multiplication between matrices and arrays:

m := matrix[4, 4]f32{
	1, 2, 3, 4, 
	5, 5, 4, 2, 
	0, 1, 3, 0, 
	0, 1, 4, 1,

v := [4]f32{1, 5, 4, 3}

// treating `v` as a column vector
fmt.println("m * v", m * v)

// treating `v` as a row vector
fmt.println("v * m", v * m)

// Support with non-square matrices
s := matrix[2, 4]f32{ // [4][2]f32 default layout
	2, 4, 3, 1, 
	7, 8, 6, 5, 

w := [2]f32{1, 2}
r: [4]f32 = w * s
fmt.println("r", r)

Component-wise operations:

// if the element type supports it
// Not support for '/', '%', or '%%' operations

a := matrix[2, 2]i32{
	1, 2,
	3, 4,

b := matrix[2, 2]i32{
	-5,  1,
	 9, -7,

c0 := a + b
c1 := a - b
c2 := a & b
c3 := a | b
c4 := a ~ b
c5 := a &~ b

// component-wise multiplication
// since a * b would be a standard matrix multiplication
c6 := hadamard_product(a, b) 

fmt.println("a + b",  c0)
fmt.println("a - b",  c1)
fmt.println("a & b",  c2)
fmt.println("a | b",  c3)
fmt.println("a ~ b",  c4)
fmt.println("a &~ b", c5)
fmt.println("hadamard_product(a, b)", c6)

Submatrix Casting #

Submatrix casting square matrices #

Casting a square matrix to another square matrix with same element type is supported.

  • If the cast is to a smaller matrix type, the top-left submatrix is taken.
  • If the cast is to a larger matrix type, the matrix is extended with zeros everywhere and ones in the diagonal for the unfilled elements of the extended matrix.
mat2 :: distinct matrix[2, 2]f32
mat4 :: distinct matrix[4, 4]f32

m2 := mat2{
	1, 3,
	2, 4,

m4 := mat4(m2)
assert(m4[2, 2] == 1)
assert(m4[3, 3] == 1)
fmt.printf("m2 %#v\n", m2)
fmt.println("m4", m4)
fmt.println("mat2(m4)", mat2(m4))
assert(mat2(m4) == m2)

b4 := mat4{
	1, 2, 0, 0,
	3, 4, 0, 0,
	5, 0, 6, 0,
	0, 7, 0, 8,
fmt.println("b4", matrix_flatten(b4))
Casting non-square matrices #

Casting a matrix to another matrix is allowed as long as they share the same element type and the number of elements (rows*columns). Matrices in Odin are stored in column-major order, which means the casts will preserve this element order.

mat2x4 :: distinct matrix[2, 4]f32
mat4x2 :: distinct matrix[4, 2]f32

x := mat2x4{
	1, 3, 5, 7, 
	2, 4, 6, 8,

y := mat4x2(x)
fmt.println("x", x)
fmt.println("y", y)

Technical Information of matrix Types #

The default internal representation of a matrix in Odin is stored in column-major format e.g. matrix[2, 3]f32 is internally [3][2]f32 (with a different alignment requirement).

Column-major is used in order to utilize (SIMD) vector instructions effectively on modern hardware, if possible.

If a row-major storage format is required, the #row_major directive can be used. e.g. #row_major matrix[2, 3]f32 is internally [2][3]f32 (with a different alignment requirement).

Unlike normal arrays, matrices try to maximize alignment to allow for the (SIMD) vectorization properties whilst keeping zero padding (either between columns (assuming default layout) or at the end of the type).

Zero padding is a compromise for use with third-party libraries, instead of optimizing for performance. Padding between columns (assuming default layout) was not taken even if that would have allowed each column to be loaded individually into a SIMD register with the correct alignment properties.

Currently, matrices are limited to a maximum of 16 elements (rows*columns), and a minimum of 1 element. This is because matrices are stored as values (not a reference type), and thus operations on them will be stored on the stack. Restricting the maximum element count minimizes the possibility of stack overflows.

Built-in Procedures (Compiler Level) in base:intrinsics and core:math/linalg:

  • transpose(m) transposes a matrix
  • outer_product(a, b) takes two array-like data types and returns the outer product of the values in a matrix
  • hadamard_product(a, b) component-wise multiplication of two matrices of the same type
  • matrix_flatten(m)
    • converts the matrix into a flatten array of elements in column-major order.
  • conj(x)
    • conjugates the elements of a matrix for complex element types only

Procedures (Runtime Level) (all square matrix procedures) in core:math/linalg:

  • determinant(m)
  • adjugate(m)
  • inverse(m)
  • inverse_transpose(m)
  • hermitian_adjoint(m)
  • matrix_trace(m)
  • matrix_minor(m)

raw_data procedure #

raw_data is a built-in procedure which returns the underlying data of a built-in data type as a Multi-Pointer.

raw_data([]$E)         -> [^]E    // slices
raw_data([dynamic]$E)  -> [^]E    // dynamic arrays
raw_data(^[$N]$E)      -> [^]E    // fixed array and enumerated arrays 
raw_data(^#simd[$N]$E) -> [^]E    // simd vectors 
raw_data(string)       -> [^]byte // 	

using statement #

using can be used to bring entities declared in a scope/namespace into the current scope. This can be applied to import names, struct fields, procedure fields, and struct values.

import "foo"
bar :: proc() {
	// imports all the exported entities from the `foo` package into this scope
	using foo

Using statement with structs #

Let’s take a very simple entity struct:

Vector3 :: struct{x, y, z: f32}
Entity :: struct {
	position: Vector3,
	orientation: quaternion128,

It can be used like this:

foo :: proc(entity: ^Entity) {
	fmt.println(entity.position.x, entity.position.y, entity.position.z)

The entity members can be brought into the procedure scope by using it:

foo :: proc(entity: ^Entity) {
	using entity
	fmt.println(position.x, position.y, position.z)

The using can be applied to the parameter directly:

foo :: proc(using entity: ^Entity) {
	fmt.println(position.x, position.y, position.z)

It can also be applied to sub-fields:

foo :: proc(entity: ^Entity) {
	using entity.position
	fmt.println(x, y, z)

We can also apply the using statement to the struct fields directly, making all the fields of position appear as if they are on Entity itself:

Entity :: struct {
	using position: Vector3,
	orientation: quaternion128,
foo :: proc(entity: ^Entity) {
	fmt.println(entity.x, entity.y, entity.z)

Subtype polymorphism #

It is possible to get subtype polymorphism, similar to inheritance-like functionality in C++, but without the requirement of vtables or unknown struct layout:

foo :: proc(entity: Entity) {
	fmt.println(entity.x, entity.y, entity.z)

Frog :: struct {
	ribbit_volume: f32,
	using entity: Entity,

frog: Frog
// Both work
frog.x = 123

Note: using can be applied to arbitrarily many things, which allows the ability to have multiple subtype polymorphism (but also its issues).

Note: using’d fields can still be referred by name.

or_else expression #

or_else is an infix binary operator that allows the user to define default values for certain expressions with optional-ok semantics.

m: map[string]int
i: int
ok: bool

if i, ok = m["hellope"]; !ok {
	i = 123
// The above can be mapped to `or_else`
i = m["hellope"] or_else 123

assert(i == 123)

or_else can be used with type assertions too, as they have optional-ok semantics.

v: union{int, f64}
i: int
i = v.(int) or_else 123
i = v.? or_else 123 // Type inference magic
assert(i == 123)

m: Maybe(int)
i = m.? or_else 456
assert(i == 456)

or_return operator #

The concept of or_return will work by popping off the end value in a multiple valued expression and checking whether it was not nil or false, and if so, set the end return value to value if possible. If the procedure only has one return value, it will do a simple return. If the procedure had multiple return values, or_return will require that all parameters be named so that the end value could be assigned to by name and then an empty return could be called.

Error :: enum {

caller_1 :: proc() -> Error {
	return .None

caller_2 :: proc() -> (int, Error) {
	return 123, .None
caller_3 :: proc() -> (int, int, Error) {
	return 123, 345, .None

foo_1 :: proc() -> Error {
	// This can be a common idiom in many code bases
	n0, err := caller_2()
	if err != nil {
		return err

	// The above idiom can be transformed into the following
	n1 := caller_2() or_return

	// And if the expression is 1-valued, it can be used like this
	caller_1() or_return
	// which is functionally equivalent to
	if err1 := caller_1(); err1 != nil {
		return err1

	// Multiple return values still work with `or_return` as it only
	// pops off the end value in the multi-valued expression
	n0, n1 = caller_3() or_return

	return .None
foo_2 :: proc() -> (n: int, err: Error) {
	// It is more common that your procedure returns multiple values
	// If `or_return` is used within a procedure that returns multiple 
	// values (2+), then all the returned values must be named 
	// so that a bare `return` statement can be used

	// This can be a common idiom in many code bases
	x: int
	x, err = caller_2()
	if err != nil {

	// The above idiom can be transformed into the following
	y := caller_2() or_return
	_ = y

	// And if the expression is 1-valued, it can be used like this
	caller_1() or_return

	// which is functionally equivalent to
	if err1 := caller_1(); err1 != nil {
		err = err1

	// If using a non-bare `return` statement is required, setting the return values
	// using the normal idiom is a better choice and clearer to read
	if z, zerr := caller_2(); zerr != nil {
		return -345 * z, zerr

	// If the other return values need to be set depending on what the end value is,
	// the `defer if` idiom can be used
	defer if err != nil {
		n = -1

	n = 123

or_continue operator #

or_continue is an operator that allows for simplified control flow in a loop. It functions much like a combination of or_return and continue in that it checks if the last value in a multiple-valued expression is false or not nil, and if so, behaves like a continue statement.

import "core:fmt"

Job :: struct {
	id:         int,
	tasks_left: int,
	result:     int,
	error_has_occurred: bool,

// Returns true if it completed its last task.
do_work_until_done :: proc(job: ^Job) -> bool {
	if job.tasks_left == 0 {
		return false

	job.result *= 3
	job.tasks_left -= 1
	return job.tasks_left == 0

// Returns a result and true if everything worked out.
// Otherwise, returns zero and false.
tally :: proc(job: ^Job) -> (int, bool) {
	if job.error_has_occurred {
		return 0, false

	return job.result, true

main :: proc() {
	jobs: [dynamic]Job
	append(&jobs, Job{ id = 1, })
	append(&jobs, Job{ id = 3, tasks_left = 2, result = 7 })
	append(&jobs, Job{ id = 5, tasks_left = 1, result = 5 })
	append(&jobs, Job{ id = 7, tasks_left = 1, result = 5, error_has_occurred = true })

	job_loop: for &job in jobs {
		do_work_until_done(&job) or_continue job_loop
		result := tally(&job)    or_continue job_loop

		fmt.printfln("Job #%i has completed its work. Result is: %i",, result)

The example above will print the following:

Job #5 has completed its work. Result is: 15

Only job #5 completes, because it has only 1 task left and its error_has_occurred is the default value, which is false in this case, as every variable in Odin is implicitly zeroed out unless made explicit.

Without or_continue, the above loop would look more like this:

// [...]
	job_loop: for &job in jobs {
		if !do_work_until_done(&job) {
			continue job_loop
		result, ok := tally(&job)
		if !ok {
			continue job_loop

		fmt.printfln("Job #%i has completed its work. Result is: %i",, result)
// [...]

The underlying operation is the same, but the code is more verbose where it doesn’t need to be. As shown in the example, or_continue also works with labels, just like continue.

or_break operator #

or_break follows the same mechanics as or_continue, except that it performs a break operation on its containing loop instead of a continue.

Conditional compilation #

A couple of ways are provided for doing this, and each of them have their uses.

File suffixes #

Often, you want to separate multiple implementations of a package based on the OS or the architecture.

Your .odin files can have a magic suffix that will cause the compiler to either include or exclude them based on the target platform or architecture, or both.

For example, foobar_windows.odin would only be compiled on Windows, foobar_linux.odin only on Linux, and foobar_windows_amd64.odin only on Windows AMD64.

Another reserved suffix is _test, which includes a file only when testing. Assume a package with foobar.odin and foobar_test.odin. Anything in foobar_test.odin will be hidden from foobar.odin, unless the odin test command is used.
Note that the entry point procedure main must not be located in a file with the _test suffix.

Please see the procedure attribute @(test) for more information.

when statements #

Sometimes you only want to include a small number of statements or declarations for compilation, if a certain compile-time expression evaluates to true. This expression can be any compile-time-known expression which results in a value of type bool.

The compiler provides a set of builtin constants which are available in all files in a compilation, and which can be used in a when condition. Here is a comprehensive list of them:

Name Description
ODIN_VERSION A string that represents the Odin compiler version being used. (e.g: dev-2023-04)
ODIN_OS, ODIN_OS_STRING An enum value, or string, respectively, indicating what the target operating system is.
ODIN_ENDIAN, ODIN_ENDIAN_STRING An enum value, or string, respectively, indicating what the endianness of the target is.
ODIN_ARCH, ODIN_ARCH_STRING An enum value, or string, respectively, indicating what the CPU architecture of the target is.
ODIN_DEBUG true if -debug command line switch is passed, which enables debug info generation.
ODIN_DISABLE_ASSERT true if -disable-assert command line switch is passed, which removes all calls to assert from the compilation.
ODIN_BUILD_MODE An enum value indicating what type of compiled output the user desires. (.Executable, .Dynamic, .Object, .Assembly, or .LLVM_IR.)
ODIN_ERROR_POS_STYLE An enum value indicating what style is being used to print the source location of compile errors and warnings. (Default, Unix.)
ODIN_DEFAULT_TO_NIL_ALLOCATOR true if -default-to-nil-allocator command lines switch is passed, which sets the initial allocator to an allocator that does nothing.
ODIN_NO_DYNAMIC_LITERALS true if -no-dynamic-literals command line switch is passed, which prohibit dynamic array or map literals.
ODIN_NO_CRT true if -no-crt command line switch is passed, which inhibits linking with the C Runtime Library, a.k.a. LibC.
ODIN_USE_SEPARATE_MODULES true if -use-separate-modules command line switch is passed, which builds each package into its own object file, and then links them together, instead of performing a unity build.
ODIN_TEST true if the code is being compiled via an invocation of odin test.
ODIN_NO_ENTRY_POINT true if -no-entry-point command line switch is passed, which makes the declaration of a main procedure optional.
ODIN_FOREIGN_ERROR_PROCEDURES true if -foreign-error-procedures command line switch is passed, which inhibits generation of runtime error procedures, so that they can be in a separate compilation unit.
ODIN_DISALLOW_RTTI true if -disallow-rtti command line switch is passed, which inhibits generation of full Runtime Type Information.
ODIN_ROOT Path to the folder containing the Odin compiler executable.
ODIN_BUILD_PROJECT_NAME Name of the folder that contains the entry point.
ODIN_VENDOR String which identifies the compiler being used. The official compiler sets this to "odin".
ODIN_VALGRIND_SUPPORT true if Valgrind integration is supported on the target.

What follows is an example of when you might use this approach. It sets the initial allocator to one that tracks memory leaks and incorrect frees when the user has asked for debug information to be emitted.

package main

import "core:fmt"
import "core:mem"

main :: proc() {
	when ODIN_DEBUG {
		track: mem.Tracking_Allocator
		mem.tracking_allocator_init(&track, context.allocator)
		context.allocator = mem.tracking_allocator(&track)

		defer {
			if len(track.allocation_map) > 0 {
				fmt.eprintf("=== %v allocations not freed: ===\n", len(track.allocation_map))
				for _, entry in track.allocation_map {
					fmt.eprintf("- %v bytes @ %v\n", entry.size, entry.location)
			if len(track.bad_free_array) > 0 {
				fmt.eprintf("=== %v incorrect frees: ===\n", len(track.bad_free_array))
				for entry in track.bad_free_array {
					fmt.eprintf("- %p @ %v\n", entry.memory, entry.location)

Command-line defines #

Sometimes you want to do something conditionally based on some compile-time parameters of some sort, but globally, across the entire project. This is how you define those.

You may define a constant using the -define command line switch. e.g: -define:FOO=true. You can then fetch its value as a constant in your code like this:

FOO :: #config(FOO, false) // defines `FOO` as a constant with the default value of false
BAR :: #config(BAR_DEBUG, true) // name can be different compared to the constant 

when FOO {
	// only evaluated when `FOO` is true
} else {
	// only evaluate when `FOO` is false

The value for a command line define may be an integer, boolean, or string. Currently, no other types are supported.

You can read up further on Built-in procedures here.

Build tags #

This feature allows you to cover more edge-case situations where you want some code to be compiled on several platforms.

However, overly-liberal use of this feature can make it hard to reason about what code is included or not, based on the target platform or architecture. File Suffixes are typically a nicer approach if they cover what you need.

For the sake of demonstration, let’s take POSIX: You could use foobar_unix.odin, which has no special meaning to the compiler at all, and use a tag in the file itself.

Here’s an example of a file that will only be included on Linux or Darwin:

//+build linux, darwin
package foobar

Implicit context system #

In each scope, there is an implicit value named context. This context variable is local to each scope and is implicitly passed by pointer to any procedure call in that scope (if the procedure has the Odin calling convention).

The main purpose of the implicit context system is for the ability to intercept third-party code and libraries and modify their functionality. One such case is modifying how a library allocates something or logs something. In C, this was usually achieved with the library defining macros which could be overridden so that the user could define what they wanted. However, not many libraries supported this in many languages by default which meant intercepting third-party code to see what it does and to change how it does it was not possible.

main :: proc() {
	c := context // copy the current scope's context

	context.user_index = 456
		context.allocator = my_custom_allocator()
		context.user_index = 123
		supertramp() // the `context` for this scope is implicitly passed to `supertramp`

	// `context` value is local to the scope it is in
	assert(context.user_index == 456)

supertramp :: proc() {
	c := context // this `context` is the same as the parent procedure that it was called from
	// From this example, context.user_index == 123
	// A context.allocator is assigned to the return value of `my_custom_allocator()`

	// The memory management procedure uses the `context.allocator` by default unless explicitly specified otherwise
	ptr := new(int)

By default, the context value has default values for its parameters which is decided in the package runtime. These defaults are compiler specific.

To see what the implicit context value contains, please see the definition of the Context struct in package runtime.

Allocators #

Odin is a manual memory management based language. This means that Odin programmers must manage their own memory, allocations, and tracking. To aid with memory management, Odin has huge support for custom allocators, especially through the implicit context system.

The built-in types of dynamic arrays and map both contain a custom allocator. This allocator can be either manually set or the allocator from the current context will be assigned to the data type.

All allocations in Odin are preferably done through allocators. The core library of Odin takes advantage of allocators through the implicit context system. The following call:

ptr := new(int)

is equivalent to this:

ptr := new(int, context.allocator)

The allocator from the context is implicitly assigned as a default parameter to the built-in procedure new.

The implicit context stores two different forms of allocators: context.allocator and context.temp_allocator. Both can be reassigned to any kind of allocator. However, these allocators are to be treated slightly differently.

  • context.allocator is for “general” allocations, for the subsystem it is used within.
  • context.temp_allocator is for temporary and short lived allocations, which are to be freed once per cycle/frame/etc.

By default, the context.allocator is an OS heap allocator and the context.temp_allocator is assigned to a scratch allocator (a growing arena based allocator). free_all(context.temp_allocator) must be called to clear the contents of the temporary allocator’s internal arena.

The following procedures are built-in (and also available in package mem with enforced allocator errors) and are encouraged for managing memory:

  • new - allocates a value of the type given. The result value is a pointer to the type given.
ptr := new(int)
ptr^ = 123
x: int = ptr^
  • new_clone - allocates a clone of the value passed to it. The resulting value of the type will be a pointer to the type of the value passed.
x: int = 123
ptr: ^int
ptr = new_clone(x)
assert(ptr^ == 123)
slice := make([]int, 65)

dynamic_array_zero_length := make([dynamic]int)
dynamic_array_with_length := make([dynamic]int, 32)
dynamic_array_with_length_and_capacity := make([dynamic]int, 16, 64)

made_map := make(map[string]int)
made_map_with_reservation := make(map[string]int, 64)
  • free - frees the memory at the pointer given. Note: only free memory with the allocator it was allocated with.
ptr := new(int)
  • free_all - frees all the memory of the context’s allocator (or given allocator). Note: not all allocators support this procedure.
  • delete - deletes the backing memory of a value allocated with make or a string that was allocated through an allocator.

To see more uses of allocators and allocation-related procedures, please see package mem in the core library.

For more information regarding memory allocation strategies in general, please see Ginger Bill’s Memory Allocation Strategy series.

Explicit context Definition #

Procedures which do not use the "odin" calling convention must explicitly assign the context if something within its body requires it.

explicit_context_definition :: proc "c" () {
	// Try commenting the following statement out below
	context = runtime.default_context()

	fmt.println("\n#explicit context definition")

dummy_procedure :: proc() {

Here is another example of setting an error callback for vendor:glfw:

error_callback :: proc "c" (code: i32, desc: cstring) {
	context = runtime.default_context() // set the current context
	fmt.println(desc, code) // fmt.* calls use the odin calling convention

Logging System #

As part of the implicit context system, there is a built-in logging system.

To see more uses of loggers, please see package log in the core library.

Foreign system #

It is sometimes necessary to interface with foreign code, such as a C library. In Odin, this is achieved through the foreign system. You can “import” a library into the code using the same semantics as a normal import declaration:

foreign import kernel32 "system:kernel32.lib"

This foreign import declaration will create a “foreign import name” which can then be used to associate entities within a foreign block.

foreign import kernel32 "system:kernel32.lib"
foreign kernel32 {
	ExitProcess :: proc "stdcall" (exit_code:  u32) ---

If a library exports global variables, you can import those into Odin as well.

foreign lib {
	x: i32

Foreign procedure declarations have the cdecl/c calling convention by default unless specified otherwise. Due to foreign procedures not having a body declared within this code, you need to append the --- symbol to the end to distinguish it as a procedure literal without a body and not a procedure type.

The attributes system can be used to change specific properties of entities declared within a block:

@(default_calling_convention = "std")
foreign kernel32 {
	@(link_name="GetLastError") get_last_error :: proc() -> i32 ---

Available attributes for foreign blocks:

default_calling_convention=<string> default calling convention for procedures declared within this foreign block
link_prefix=<string> prefix that needs to be appended to the linkage names of the entities except where the link name has been explicitly overridden

Using a vendor library #

As described in the Foreign System we often want to use existing C libraries. Odin has a wide collection of maintained bindings and ports.

Note: Case notation should remain the same as the original authors intended, to make porting code easier.

Let’s run through how we could use the vendor:glfw library. The code will be based on their Quick Guide but we will simplify it to only show using glfw.

package main

import "base:runtime"
import "core:fmt"
import "vendor:glfw"

error_callback :: proc "c" (code: i32, desc: cstring) {
	context = runtime.default_context()
	fmt.println(desc, code)

key_callback :: proc "c" (window: glfw.WindowHandle, key, scancode, action, mods: i32) {
	if key == glfw.KEY_ESCAPE && action == glfw.PRESS {
		glfw.SetWindowShouldClose(window, glfw.TRUE)

main :: proc() {

	if !glfw.Init() {
	defer glfw.Terminate()

	glfw.WindowHint(glfw.CONTEXT_VERSION_MAJOR, 2)
	glfw.WindowHint(glfw.CONTEXT_VERSION_MINOR, 0)

	window := glfw.CreateWindow(640, 480, "Simple example", nil, nil)
	if window == nil {
	defer glfw.DestroyWindow(window)

	glfw.SetKeyCallback(window, key_callback)

	// ...
	// ...

	for !glfw.WindowShouldClose(window) {
		// ...


As we can see there is little difference to how someone would use vendor:glfw in this case. It’s not always perfect but often good enough to port existing code quickly.

Parametric polymorphism #

Parametric polymorphism, commonly referred to as “generics”, allow the user to create a procedure or data that can be written generically so it can handle values in the same manner.

Note: Within the Odin code base and documentation, the nickname “parapoly” is usually used.

Explicit parametric polymorphism #

Explicit parametric polymorphism means that the types of the parameters of a proc or of the data fields of a struct (when intended to potentially be used with multiple possible types) must be explicitly provided. This is similar to how C++ allows the use of templates to fill out the body of a procedure or data structure with the types that are given at compile-time as input to the template parameters, but in Odin explicit parametric polymorphism is safer and cleaner to work with.

Procedures using explicit parametric polymorphism (parapoly) #

As a reminder, all parameters passed into a function are immutable in the sense that they can’t have their value changed using = directly. A useful idiom is var := var, which expresses a variable shadowing itself. When used at the top of a procedure the compiler understands the use case of enabling local modification of the otherwise immutable parameter variable, and won’t complain about the shadowing when you compile with -vet.

sin_tau :: proc(angle_in_cycles: f64) -> f64 {
    angle_in_cycles := angle_in_cycles   // Allows `angle_in_cycles` to have its value changed
    TAU :: 2 * math.PI
    angle_in_cycles *= TAU
    return math.sin(angle_in_cycles)
assert(math.abs(sin_tau(0.25) - 1) <= 0.001)   // sin_tau(0.25) is approximately 1
assert(math.abs(sin_tau(0.75) - -1) <= 0.001)  // sin_tau(0.75) is approximately -1

However, to specify that a parameter must be a compile-time constant, which is not the same thing as an immutable parameter, and may sometimes be necessary (e.g. for parapoly) or desirable (e.g. to enforce compile-time computation), the parameter’s name must be prefixed with a dollar sign $. The following example takes two compile-time constant parameters and then uses them to initialize an array of known length:

make_f32_array :: #force_inline proc($N: int, $val: f32) -> (res: [N]f32) {
	for _, i in res {
		res[i] = val*val

array := make_f32_array(3, 2)

Types can also be explicitly passed by specifying that the typeid parameter is constant:

my_new :: proc($T: typeid) -> ^T {
	return (^T)(alloc(size_of(T), align_of(T)))

ptr := my_new(int)

Data types using explicit parametric polymorphism (parapoly) #

Structures and unions may have polymorphic parameters and the syntax for doing so is similar to procedure call syntax. Parapoly struct:

Table_Slot :: struct($Key, $Value: typeid) {
	occupied: bool,
	hash:    u32,
	key:     Key,
	value:   Value,
slot: Table_Slot(string, int)

Parapoly union:

Error :: enum {Foo0, Foo1, Foo2}
Param_Union :: union($T: typeid) #no_nil {T, Error}
r: Param_Union(int)
r = 123
r = Error.Foo0

The $ prefix is optional for record data types as all parameters must be “constant”.

Implicit parametric polymorphism #

Implicit implies that the type of a parameter is inferred from its input. In this case, the dollar sign $ can be placed on the type.

Note: Within the Odin code base and documentation, the name “polymorphic name” is usually used.

Procedures using implicit parametric polymorphism (parapoly) #

foo :: proc($N: $I, $T: typeid) -> (res: [N]T) {
	// `N` is the constant value passed
	// `I` is the type of `N`
	// `T` is the type passed
	fmt.printf("Generating an array of type %v from the value %v of type %v\n",
			   typeid_of(type_of(res)), N, typeid_of(I))
	for i in 0..<N {
		res[i] = i*i

T :: int
array := foo(4, T)
for v, i in array {
	assert(v == T(i*i))

Specialization #

In some cases, you may want to specify that a type must be a specialization of a certain type.

// Only allow types that are specializations of a (polymorphic) slice
make_slice :: proc($T: typeid/[]$E, len: int) -> T {
	return make(T, len)
Table_Slot :: struct($Key, $Value: typeid) {
	occupied: bool,
	hash:     u32,
	key:      Key,
	value:    Value,
Table :: struct($Key, $Value: typeid) {
	count:     int,
	allocator: mem.Allocator,
	slots:     []Table_Slot(Key, Value),

// Only allow types that are specializations of `Table`
allocate :: proc(table: ^$T/Table, capacity: int) {

// find :: proc(table: ^$T/Table, key: T.Key) -> (T.Value, bool) {
find :: proc(table: ^Table($Key, $Value), key: Key) -> (Value, bool) {

where clauses #

A bound on polymorphic parameters to a procedure or record can be expressed using a where clause immediately before opening {, rather than at the type’s or constant’s first mention. Additionally, where clauses can apply bounds to arbitrary types, rather than just polymorphic type parameters.

Some cases that a where clause may be useful:

  • Sanity checks for parameters:
simple_sanity_check :: proc(x: [2]int)
	where len(x) > 1,
		  type_of(x) == [2]int {
  • Parameter polymorphism checks for procedures:
cross_2d :: proc(a, b: $T/[2]$E) -> E
	where intrinsics.type_is_numeric(E) {
	return a.x*b.y - a.y*b.x
cross_3d :: proc(a, b: $T/[3]$E) -> T
	where intrinsics.type_is_numeric(E) {
	x := a.y*b.z - a.z*b.y
	y := a.z*b.x - a.x*b.z
	z := a.x*b.y - a.y*b.x
	return T{x, y, z}

a := [2]int{1, 2}
b := [2]int{5, -3}
fmt.println(cross_2d(a, b))

x := [3]f32{1, 4, 9}
y := [3]f32{-5, 0, 3}
fmt.println(cross_3d(x, y))

// Failure case
// i := [2]bool{true, false}
// j := [2]bool{false, true}
// fmt.println(cross_2d(i, j))
  • Solving disambiguations with polymorphic procedures in a procedure grouping:
foo :: proc(x: [$N]int) -> bool
	where N > 2 {
	fmt.println(#procedure, "was called with the parameter", x)
	return true

bar :: proc(x: [$N]int) -> bool
	where 0 < N,
		  N <= 2 {
	fmt.println(#procedure, "was called with the parameter", x)
	return false

baz :: proc{foo, bar}

x := [3]int{1, 2, 3}
y := [2]int{4, 9}
ok_x := baz(x)
ok_y := baz(y)
assert(ok_x == true)
assert(ok_y == false)
  • Restrictions on parametric polymorphic parameters for record types:
Foo :: struct($T: typeid, $N: int)
	where intrinsics.type_is_integer(T),
	      N > 2 {
	x: [N]T,
	y: [N-2]T,

T :: i32
N :: 5
f: Foo(T, N)
#assert(size_of(f) == (N+N-2)*size_of(T))

-> operator (selector call expressions) #

The -> operator is called the selector call expression operator and is extremely useful for call procedures stored in vtables. Component Objective Model (COM) APIs is a great example of where this kind of thing is extremely useful (such as the Direct3D11 package).

// is equivalent to
x.y(x, 123)

As the -> operator is effectively syntactic sugar, all of the same semantics still apply, meaning subtyping through using will still work as expected to allow for the emulation of type hierarchies.

Attributes #

Attributes modify the compilation details or behaviour of declarations.

General attributes #

@(private) #

Prevents a top level element from being exported with the package.

my_variable: int // cannot be accessed outside this package
@private // parenthesis can be dropped on no arguments  
my_other_variable: int

You may also make an entity private to the file instead of the package.

my_variable: int // cannot be accessed outside this file

@(private) is equivalent to @(private="package").

Using //+private in a file at the package declaration will automatically add @(private) to everything in the file

package foo

And //+private file will be equivalent to automatically adding @(private="file") to each declaration. This means that to remove the private-to-file association, you must apply a private-to-package attribute @(private) to the declaration.

@(require) #

Requires that the declaration is added to the final compilation and not optimized out.

Linking and foreign attributes #

This attribute can be attached to variable and procedure declarations inside a foreign block. This specifies what the variable/proc is called in the library. Example:

foreign foo {
    @(link_name = "bar")
    testbar :: proc(baz: int) ---

This attribute can be attached to a foreign block to specify a prefix to all names. So if functions are prefixed with ltb_ in the library is you can attach this and not specify that on the procedure on the Odin side. Example:

@(link_prefix = "ltb_")
foreign foo {
    testbar :: proc(baz: int) --- // This now refers to ltb_testbar

@export or @(export=true/false) #

Exports a variable or procedure symbol, useful for producing DLLs.

@(linkage=<string>) #

Allows the ability to specify the specific linkage of a declaration. Allow linkage kinds: "internal", "strong", "weak", and "link_once".

@(default_calling_convention=<string>) #

This attribute can be attached to a foreign block to specify the default calling convention for all procedures in the block. Example:

@(default_calling_convention = "std")
foreign kernel32 {
    @(link_name="LoadLibraryA") load_library_a  :: proc(c_str: ^u8) -> Hmodule ---

Specify the link section for a global variable.

my_global: i32

@(extra_linker_flags=<string>) #

Provide additional linker flags to a foreign import declaration.

foreign import lib {

Procedure attributes #

(deferred_*=<proc>) #

  • (deferred_in=<proc>)
  • (deferred_out=<proc>)
  • (deferred_in_out=<proc>)
  • (deferred_none=<proc>)

These attributes can be attached to a procedure X which will be called at the end of the calling scope for Xs caller. deferred_in will receive the same parameters as the called proc. deferred_out will receive the result of the called proc. deferred_in_out will receive both. deferred_none will receive no parameters.

baz :: proc() {
    fmt.println("In baz")

bar :: proc() {
    fmt.println("In bar")

foo :: proc() {
    fmt.println("Entered foo")
    fmt.println("Leaving foo")
// Prints:
// Entered foo
// In bar
// Leaving foo
// In baz

@(deprecated=<string>) #

Mark a procedure as deprecated. Running odin build/run/check will print out the message for each usage of the deprecated proc.

@(deprecated="'foo' deprecated, use 'bar' instead")
foo :: proc() {

@(require_results) #

Ensures procedure return values are acknowledged, meaning that in any scope where a procedure p having procedure attribute @(require_results) is called, the scope must explicitly handle the return values of procedure p in some way, such as by storing the return values of p in variables or explicitly dropping the values by setting _ equal them.

foo :: proc() -> bool {
    return true

main :: proc() {
    foo() // won't compile
    _ = foo() // Ok

@(warning=<string>) #

Produces a warning when a procedure is called.

@(disabled=<boolean>) #

If the provided boolean is set, the procedure will not be used when called.

@(init) #

This attribute may be applied to any procedure that neither takes any parameters nor returns any values. All suitable procedures marked in this way by @(init) will then be called at the start of the program before main is called. The exact order in which all such intialization functions are called is deterministic and hence reliable. The order is determined by a topological sort of the import graph and then in alphabetical file order within the package and then top down within the file.

@(cold) #

A hint to the compiler that this procedure is rarely called, and thus “cold”.

@(optimization_mode=<string>) #

Set the optimization mode of a procedure. Valid modes are "none", "minimal", "size", and "speed".

skip_whitespace :: proc(t: ^Tokenizer) {
    for {
        switch {
        case ' ', '\t', '\r', '\n':

@(test) #

Allows procedures with the attribute @(test) to be run with the command odin test directly.

import "core:testing"

foo :: proc(_: ^testing.T) {

Variable attributes #

@(static) #

This attribute can be applied to a variable to have it keep its state even when going out of scope. This is the same behavior as a static local variable in C.

test :: proc() -> int {
    @(static) foo := 0
    foo += 1
    return foo

main :: proc() {
    fmt.println(test()) // prints 1
    fmt.println(test()) // prints 2
    fmt.println(test()) // prints 3

@(thread_local) #

Can be applied to a variable at file scope

@(thread_local) foo: int

Specialized attributes #

  • @(builtin) Marks builtin procs in Odin’s “base:runtime” package. Cannot be used in user code.

  • @(objc_name=<string>)

  • @(objc_type=<type>)

  • @(objc_is_class_method=<boolean>)

  • @(require_target_feature=<string>)

  • @(enable_target_feature=<string>)

Directives #

Directives are a way of extending the core behaviour of the Odin programming language. They have the form #directive_name.

Record memory layout #

#packed #

This tag can be applied to a struct. Removes padding between fields that’s normally inserted to ensure all fields meet their type’s alignment requirements. Fields remain in source order.

This is useful where the structure is unlikely to be correctly aligned (the insertion rules for padding assume it is), or if the space-savings are more important or useful than the access speed of the fields.

Accessing a field in a packed struct may require copying the field out of the struct into a temporary location, or using a machine instruction that doesn’t assume the pointer address is correctly aligned, in order to be performant or avoid crashing on some systems. (See intrinsics.unaligned_load.)

struct #packed {x: u8, y: i32, z: u16, w: u8}

#raw_union #

This tag can be applied to a struct. Struct’s fields will share the same memory space which serves the same functionality as unions in C language. Useful when writing bindings especially.

struct #raw_union {u: u32, i: i32, f: f32}

#align #

This tag can be applied to a struct or union. When #align is passed an integer N (as in #align N), it specifies that the struct will be aligned to N bytes. The struct’s fields will remain in source-order.

Foo :: struct #align(4) {
    b: bool,
Bar :: union #align(4) {

#no_nil #

This tag can be applied to a union to not allow nil values.

A :: union {int, bool}
B :: union #no_nil {int, bool}
// Possible states of A:
{} // nil

// Possible states of B:
{int} // default state

Control statements #

#partial #

By default all cases of an enum or union have to be covered in a switch statement. The reason for this requirement is because it makes accidental bugs less likely. However, the #partial tag allows you to not have to write out cases that you don’t need to handle:

Foo :: enum {

test :: proc() {
    bar := Foo.A

    // All cases required, removing any would result in an error
    switch bar {
    case .A:
    case .B:
    case .C:

    // Partially state wanted cases
    #partial switch bar {
    case .A:
    case .B:

The #partial directive can also be used to initialize an enumerated array.

Procedure parameters #

#no_alias #

This tag can be applied to a procedure parameter that is a pointer. This is a hint to the compiler that this parameter will not alias other parameters. This is equivalent to C’s __restrict.

foo :: proc(#no_alias a, b: ^int) {}

#any_int #

This tag can be applied to a procedure parameter that is an integer. This allows implicit casts to the procedures integer type at the call site.

foo :: proc(#any_int a: int) {}
x : i32
foo(x) // This is now allowed without an explicit cast

#caller_location #

This tag is used as a function’s parameter value. In the following function signature,

alloc :: proc(size: int, alignment: int = DEFAULT_ALIGNMENT, loc := #caller_location) -> rawptr

loc is a variable of type Source_Code_Location (see base/runtime/core.odin) that is automatically filled with the location of the line of code calling the function (in this case, the line of code calling alloc).

#c_vararg #

Used to interface with vararg functions in foreign procedures.

foreign foo {
    bar :: proc(n: int, #c_vararg args: ..any) ---

#by_ptr #

Used to interface with const reference parameters in foreign procedures. The parameter is passed by pointer internally.

foreign foo {
    bar :: proc(#by_ptr p: T) ---

to represent

void bar(const T*)

#optional_ok #

Allows skipping the last return parameter, which needs to be a bool

import "core:fmt"

foo :: proc(x: int) -> (value: int, ok: bool) #optional_ok {
    return x + 1, true

main :: proc() {
    for x := 0; x < 11; x = foo(x) {
        fmt.printf("v: %v\n", x)

#optional_allocator_error #

Allows skipping the last return parameter, which needs to be a runtime.Allocator_Error

import "base:runtime"
import "core:strings"
import "core:fmt"

add_greetings :: proc(name: string) -> (string, runtime.Allocator_Error) #optional_allocator_error {
	result, err := strings.join({"Hello", name}, ", ")
	return result, err

main :: proc() {
	msg := add_greetings("Bill")

Expressions #

#type #

This tag doesn’t serve a functional purpose in the compiler, this is for telling someone reading the code that the expression is a type. The main case is for showing that a procedure signature without a body is a type and not just missing its body, for example:

foo :: #type proc(foo: string)

bar :: struct {
    gin: foo,

Statements #

#bounds_check and #no_bounds_check #

The #bounds_check and #no_bounds_check flags control Odin’s built-in bounds checking of arrays and slices. Any statement, block, or function with one of these flags will have their bounds checking turned on or off, depending on the flag provided. Valid uses of these flags include:

proc_without_bounds_check :: proc() #no_bounds_check {
    #bounds_check {
        #no_bounds_check fmt.println(os.args[1])

Built-in procedures #

#assert(<boolean>) #

Unlike assert, #assert runs at compile-time. #assert breaks compilation if the given bool expression is false, and thus #assert is useful for catching bugs before they ever even reach run-time. It also has no run-time cost.


#panic(<string>) #

Panic runs at compile-time. It is functionally equivalent to an #assert with a false condition, but #panic has an error message string parameter.


#config(<identifer>, default) #

Checks if an identifier is defined through the command line, or gives a default value instead.

Values can be set with the -define:NAME=VALUE command line flag.

#defined #

Checks if an identifier is defined. This may only be used within a procedure’s body.

n: int
when #defined(n) { fmt.println("true") }
if #defined(int) { fmt.println("true") }
when #defined(nonexistent_proc) == false { fmt.println("proc was not defined") }

#file, #line, #procedure #

Return the current file path, line number, or procedure name, respectively. Used like a constant value. file_name :: #file

#location() or #location(<entity>) #

Returns a runtime.Source_Code_Location (see base/runtime/core.odin). Can be called with no parameters for current location, or with a parameter for the location of the variable/proc declaration.

foo :: proc() {}

main :: proc() {
    n: int

#load(<string-path>) or #load(<string-path>, <type>) #

Returns a []u8 of file contents at compile time, or optionally as another type.

foo := #load("path/to/file")
bar := #load("path/to/file", string)

// If a file's size is not a multiple of the `size_of(type)`, then any remainder is ignored.
baz := #load("path/to/file", []f32)

#load also works with or_else to provide default content when the file wasn’t found

foo := #load("path/to/file", string) or_else "Hellope"

#load_hash(<string-path>, <string-hash>) #

Returns a constant integer of the hash of a file’s contents at compile time. Available hashes: "adler32", "crc32", "crc64", "fnv32", "fnv64", "fnv32a", "fnv64a", "murmur32", or "murmur64".

hash :: #load_hash("path/to/file", "crc32")

Useful idioms #

The following are useful idioms which are emergent from the semantics of the language.

Basic idioms #

Ternary operator #

The following two snippets are identical:

bar := condition ? 1 : 42
bar := 1 if condition else 42

You can also use ternary expressions with constants at compile-time:

DEBUG_LOG_SIZE :: 1024 when ODIN_DEBUG else 0

If-statements with initialization #

if str, ok := value.(string); ok {
} else {

Iterating through slices of structs by value or by reference #

Foo :: struct {
	f: f32,
	i: i32,

foos := make([]Foo, num)

// By-value basic ranged-based loop, with implicit indexing
for v, j in foos {
	using v
	fmt.println(j, v, f, i)

// Alternative range-based loop, with explicit indexing
for _, j in foos {
	using foo := foos[j] // copy
	fmt.println(j, foo, f, i)

// By-reference range-based explicit indexing loop
for _, j in foos {
	using foo := &foos[j] // "reference", changes to `f` or `i` are visible outside this scope
	fmt.println(j, foo, f, i)

// By-reference range-based through pointer
for &v, j in foos {
	using v // `v` is now a variable reference as `foos` was passed by pointer
	fmt.println(j, foo, f, i)

‘defer if’ #

cond := true

defer if cond {
	fmt.println("Hello World") // "Hello world" last

fmt.println("Hellope") // "Hellope" first

‘Maybe(T)’ #

Maybe(T) is a union which either returns a type T or nil. In other languages this is often seen as Option(T), Result(T), etc.

Odin has multiple return values, so Maybe(T) is used less frequently or rarely in the core library. Instead of doing -> Maybe(int) you could transform it to -> (int, bool).

halve :: proc(n: int) -> Maybe(int) {
	if n % 2 != 0 do return nil
	return n / 2

half, ok := halve(2).?
if ok do fmt.println(half)       // 1
half, ok = halve(3).?
if !ok do fmt.println("3/2 isn't an int")

n := halve(4).? or_else 0
fmt.println(n)                   // 2

Advanced idioms #

Subtype polymorphism with run-time type-safe down-casting:

Entity :: struct {
	id:   u64,
	name: string,

	variant: union{^Frog},

Frog :: struct {
	using entity: Entity,
	volume: f32,
	jump_height: i32,

new_entity :: proc($T: typeid) -> ^T {
	e := new(T)
	e.variant = e
	return e

entity: ^Entity = new_entity(Frog)
switch e in entity.variant {
case ^Frog:
	fmt.println("Ribbit:", e.volume)

Implicit Type Conversions #

Odin is a strongly and distinctly typed language by default. It has very few implicit type conversions compared to many other languages.

  • ^T -> rawptr
  • [^]T -> rawptr
  • [^]T <-> ^T
  • All types to any (must be specialized/non-polymorphic)
  • Any of its variants to the union
  • fN -> complex2N (e.g. f32 -> complex64)
  • fN -> quaternion4N (e.g. f32 -> quaternion128)
  • complex2N -> quaternion4N (e.g. complex64 -> quaternion128)
  • T -> [N]T
  • T -> matrix[R, C]T
  • T -> #simd[N]T
  • distinct proc <-> proc (same base types)
  • distinct matrix <-> matrix (same base types)
  • Subtypes through using
  • Untyped integers -> all numeric related types that can represent them without truncation
  • Untyped floats -> all numeric related types that can represent them without truncation
  • Untyped booleans -> all boolean related types
  • Untyped rune -> all rune types
  • Untyped strings -> all string types

Extra Information #

More details can be found on the Github wiki for Odin. Some of this information includes:

What to do if you get stuck #

If you are unable to find the information you need on this overview page, the FAQ, the wiki, the example repository (which contains demos for using the vendor libs, e.g. Tetris in raylib), or the package documentation, then you will likely find it very helpful to explore your Odin source code directory, especially the files contained in the following five subdirectories: examples\demo, tests, core, vendor, and misc\old_demos.

The following list describes why each of these may be useful:

  • The examples\demo\demo.odin file contains ~2500 lines of Odin code that demonstrate many of Odin’s language features and provide commentary on some of them. This file contains many examples that cannot be found anywhere in the Overview nor in the other documentation.
  • The tests folder provides unit tests for many of Odin’s features and libraries, whereby reading these files you can gain a more nuanced view of exactly how things are intended or expected to behave. Tests are essentially automatically verified documentation. Tests often cover details that normal documentation doesn’t even mention. Tests are also guaranteed to be up-to-date (if regularly run), unlike more informal documentation.
  • The core and vendor folders contain the bindings and implementation code for Odin’s standard library and various multimedia libraries respectively. Even if you don’t understand the implementation of something, reading the code can still greatly improve your chances of guessing what exactly it really does. Odin is a straightforward and legible language with relatively little magic compared to other modern languages. Reading source code can enable you to work around missing documentation much more effectively. This is a very useful thing to keep in mind for working with any under-development language or library effectively.
  • misc\old_demos may contain examples that are different from the main up-to-date demo.odin file contained in examples\demo. This may provide additional context for Odin’s design and features. The other resources are probably better though.

Try doing a text search in one or more of these subdirectories for what you are looking for. Make sure the search is a proper full text search too, such as what grep (a popular 3rd party file search program) provides. Be careful that you specify your search correctly, especially if you use regex. Some default searches on some operating systems may miss content that exists in some files by not searching the actual file contents completely or at all, which can be misleading.

Odin’s documentation may be sparse at times, but this sparsity can be worked around effectively by using the above listed resources. Don’t forget they exist.

When working with any system that is still under-development these kinds of techniques are essential for maximizing your effectiveness. Many (perhaps most) real world companies, especially in intense industries such as game development and multimedia often don’t have complete documentation and changes can happen rapidly.

Self-sufficiency in such a context requires a willlingness to explore these kinds of resources proactively, rather than waiting for documentation that may be slow to come or may not fully cover what things actually do precisely enough.

Don’t be afraid to simply experiment and try to deduce what something is really doing or what features may exist. You may be surprised how much you can still accomplish with just a little bit of patience and thoughtfulness!

Furthermore, even if Odin doesn’t yet have a feature or library that you need, the fact that Odin has bindings to C’s standard library (which are available in the libc package via import "core:c/libc") means that any algorithms, example code, documentation, or books originally written for C can also be used to accomplish what you need in Odin. You can then optionally write Odin wrappers around that code to bridge the idiomatic gap better or else just use the C-like code directly. You can also bind to code from any libraries or languages that foreign can bind to (see the foreign section for more info).

Thus, when necessity calls for it, the entire literature and community of C is still (in effect) available to you in Odin as well. So, any time you are tempted to think “I can’t implement this in Odin yet because there’s not enough documentation” remind yourself that all (or almost all) of C is still available to you, but through a cleaner namespaced interface. Odin is also similar to C anyway, so direct translations of C to Odin (without even using the libc bindings) may still be relatively easy. In effect, any tutorial or book on C can also be thought of as an Odin resource too in that sense!

You can also make your experience navigating Odin code easier by installing a syntax highlighter and/or a language server, which do exist for some editors (e.g. VS Code, Vim, Sublime Text, and Emacs) and work well enough to make using Odin comfortable. See the list of text editors that have support for Odin code for known examples.

Finally, you can ask for information from the Odin community on Discord or elsewhere. There is also an old Handmade Network forum that is no longer in use and doesn’t have many threads, but may still have a small amount of useful info on it.

There’s a collection of other libraries created by the Odin community that may also be helpful.

Good luck and have fun!