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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 recommend to read the Getting started with Odin[1] guide.
1: https://github.com/odin-lang/Odin/wiki#getting-started-with-odin
To begin this tour, let us start with a modified version of the famous "hello world" program:
package main
import "core:fmt"
main :: proc() {
fmt.println("Hellope!");
}
Save this code to the file "hellope.odin". Now compile and run it:
odin run hellope.odin
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 hellope.odin
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 literals are enclosed in double quotes and character literals in single quotes. Special characters are escaped with a backslash `\`.
"This is a string" 'A' '\n' // newline character "C:\\Windows\\notepad.exe"
Raw string literals are enclosed in single back ticks.
`C:\Windows\notepad.exe`
The length of a string can be found using the built-in `len` proc:
len("Foo")
len(some_string)
If the string passed to `len` is a compile-time constant, the value from `len` will be a compile-time constant.
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 of type `int` x = 1; // `1` is an untyped integer literal which can implicitly convert to `int`
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.
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;
x: int = 123; x: = 123; // default type for an integer literal is `int` x := 123;
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[2] and Ginger Bill's article On the Aesthetics of the Syntax of Declarations[3].
3: https://www.gingerbill.org/article/2018/03/12/on-the-aesthetics-of-the-syntax-of-declarations/
Every Odin program is made up of packages. Programs begin running in the package `main`.
The following program imports the 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.
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
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.
@(private) my_variable: int; // cannot be accessed outside this package.
You may also make an entity private to *the file* instead of the package.
@(private="file") my_variable: int; // cannot be accessed outside this file.
`@(private)` is equivalent to `@(private="package")`.
Odin has only one loop statement, the `for` loop.
A basic `for` loop has three components separated by semicolons:
The loop will stop executing when the condition is evaluated to `false`.
for i := 0; i < 10; i += 1 {
fmt.println(i);
}
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 {
}
The basic for loop
for i := 0; i < 10; i += 1 {
fmt.println(i);
}
can also be written
for i in 0..<10 {
fmt.println(i);
}
// or
for i in 0..9 {
fmt.println(i);
}
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 {
fmt.println(character);
}
for value in some_array {
fmt.println(value);
}
for value in some_slice {
fmt.println(value);
}
for value in some_dynamic_array {
fmt.println(value);
}
for value in some_map {
fmt.println(value);
}
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. The following idiom is useful for iterating over a container in a by-reference manner:
for _, i in some_slice {
some_slice[i] = something;
}
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");
}
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.
package main
import "core:fmt"
import "core:os"
main :: proc() {
switch arch := ODIN_ARCH; arch {
case "386":
fmt.println("32 bit");
case "amd64":
fmt.println("64 bit");
case: // default
fmt.println("Unsupported 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");
case:
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:
fmt.println("units");
case 10..<13:
fmt.println("pre-teens");
case 13..<20:
fmt.println("teens");
case 20..<30:
fmt.println("twenties");
}
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;
}
fmt.println(x);
x = 234;
}
You can defer an entire block too:
{
defer {
foo();
bar();
}
defer if cond {
bar();
}
}
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 := os.open("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.
The `when` statement is almost identical to the `if` statement but with some differences:
Example:
when ODIN_ARCH == "386" {
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.
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 {
case:
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
}
}
As in many programming languages, a `continue` statement starts the next iteration of a loop prematurely:
for cond {
if get_foo() {
continue;
}
fmt.println("Hellope");
}
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:
foo();
fallthrough;
case 1:
bar();
}
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));
For more information regarding value declarations in general, please see the Odin FAQ[4].
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. The procedure always gets a copy of the thing that has been passed, as if there was an assignment statement to the procedure parameter.
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).
Parameters in a procedure body will be mutable, but as they are copies, they will not affect the original values.
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
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;
return;
}
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);
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);
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};
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:
foo :: proc{
foo_bar,
foo_baz,
foo_baz2,
another_thing_entirely,
};
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
f32 f64 // floating point numbers
complex64 complex128 // complex numbers
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
rawptr
// runtime type information specific type
typeid
any
The `int`, `uint`, and `uintptr` types are pointer sized. 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
Variables declared without an explicit initial value are given their *zero* value.
The zero value is:
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.
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.
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 is some contexts but has the same semantic meaning.
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.
In the Odin type system, certain expressions will have an "untyped" type. An untyped type can implicitly convert to a "typed" type. The following are the
The `auto_cast` operator automatically casts an expression to the destination's type if possible:
x: f32 = 123; y: int = auto_cast x;
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.
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)
You can alias a named type with another name:
My_Int :: int; #assert(My_Int == int);
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{});
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 {
fmt.println(x[i]);
}
The notation `x[i]` is used to access the i-th element of `x`; and 0-index based (like C).
The built-in `len` proc returns the array's length.
x: [5]int; #assert(len(x) == 5);
Array access is always bounds checked (at compile-time 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.
Odin's fixed length arrays support array programming[5].
5: https://en.wikipedia.org/wiki/Array_programming
Example:
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
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);
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}
For the array:
a: [6]int;
these slice expressions are equivalent:
a[0:6] a[:6] a[0:] a[:]
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!");
}
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.
It is common to append new elements to a dynamic array; this can be done so with the built-in `append` proc.
x: [dynamic]int; append(&x, 123); append(&x, 4, 1, 74, 3); // append multiple values at once
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
Slices and dynamic arrays can be deleted with the built-in `delete` proc.
delete(a); delete(b); delete(c);
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 {
A,
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
Odin supports implicit selector expressions for enums:
Foo :: enum {A, B, C};
f: Foo;
f = .A;
BAR :: bit_set[Foo]{.B, .C};
switch f {
case .A:
fmt.println("foo");
case .B:
fmt.println("bar");
case .C:
fmt.println("baz");
}
`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;
using Bar :: enum {X, Y, Z};
x := X;
}
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:
.member_name
For example:
Direction :: enum{North, East, South, West};
d: Direction;
d = Direction.East;
d = .East;
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:
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));
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 to 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
p: ^int; // ^ on the left x := p^; // ^ on the right
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;
fmt.println(v.x);
Struct fields can be accessed through a struct pointer:
v := Vector2{1, 2};
p := &v;
p.x = 1335;
fmt.println(v);
We could write `p^.x`, however, it is to nice abstract the ability to not explicitly dereference the pointer. This is very useful when refactoring code to use a pointer rather than a value, and vice versa.
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 tagged 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
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 {
bool,
i32,
f32,
string,
}
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);
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);
case:
// Default case
// In this case, it is `nil`
}
The `#no_nil` tag can be applied to the union type to state that it does not have a `nil` value, and the first variant is its default type:
Value :: union #no_nil {bool, string};
v: Value;
_, ok := v.(bool);
assert(ok);
This is useful in very limited cases, and if it is added, there must be at least two variants.
Unions also have the `#align` tag, like structures:
union #align 4 {...} // align to 4 bytes
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; fmt.println(m["Bob"]);
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
or
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,
};
A procedure type is internally a pointer to a procedure in memory. `nil` is the zero value a procedure type.
Examples:
proc(x: int) -> bool proc(c: proc(x: int) -> bool) -> (i32, f32)
Odin supports the following calling conventions:
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.
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 "core:runtime"
main :: proc() {
u := u8(123);
id := typeid_of(type_of(u));
info: ^runtime.Type_Info;
info = type_info_of(id);
}
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.
`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;
}
Let's take a very simple entity struct:
Vector3 :: struct{x, y, z: f32};
Entity :: struct {
position: Vector3,
orientation: quaternion128,
}
It can 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 on `Entity` itself:
Entity :: struct {
using position: Vector3,
orientation: quaternion128,
}
foo :: proc(entity: ^Entity) {
fmt.println(entity.x, entity.y, entity.z);
}
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;
foo(frog);
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 he 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 use the `context.allocator` by default unless explicitly specified otherwise
ptr := new(int);
free(ptr);
}
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 following definition in package runtime[6].
6: https://github.com/odin-lang/Odin/blob/master/core/runtime/core.odin#L215
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.
By default, the `context.allocator` is a OS heap allocator and the `context.temp_allocator` is assigned to a scratch allocator (a ring-buffer based allocator).
The following procedures are built-in (and also available in `package mem`) and are encouraged for managing memory:
ptr: rawptr = alloc(64); // allocate 64 bytes aligned to the default alignment x := alloc(128, 16); // allocate 128 bytes aligned to 16 bytes i := cast(^int)alloc(size_of(int), align_of(int)); // the equivalent of the `new` procedure explained next
ptr := new(int); ptr^ = 123; x: int = ptr^;
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);
ptr := new(int); free(ptr);
free_all(); free_all(context.temp_allocator); free_all(my_allocator);
delete(my_slice); delete(my_dynamic_array); delete(my_map); delete(my_string); delete(my_cstring);
ptr := alloc(16); ptr = realloc(ptr, 32);
To see more uses of allocators, please see `package mem`[7] in the core library.
7: https://github.com/odin-lang/Odin/tree/master/core/mem
For more information regarding memory allocation strategies in general, please see Ginger Bill's Memory Allocation Strategy[8] series.
8: https://www.gingerbill.org/series/memory-allocation-strategies/
As part of the implicit `context` system, there is a built-in logging system.
To see more uses of loggers, please see `package log`[9] in the core library.
9: https://github.com/odin-lang/Odin/tree/master/core/log
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) ---;
}
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
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 means that the types of the parameters must be explicitly provided.
To specify that a parameter is "constant", the parameters name must be prefixed with a dollar sign `
make_f32_array :: inline proc($N: int, $val: f32) -> (res: [N]f32) {
for _, i in res {
res[i] = val*val;
}
return;
}
array := make_f32_array(3, 2);
Types can also be explicitly passed with specifying that the `typeid` parameter is constant:
my_new :: proc($T: typeid) -> ^T {
return (^T)(alloc(size_of(T), align_of(T)));
}
ptr := my_new(int);
Structures and unions may have polymorphic parameters. The `
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;
Implicit implies that the type of a parameter is inferred from its input. In this case, the dollar sign `
Note: Within the Odin code base and documentation, the name "polymorphic name" is usually used.
foo :: proc($N: $I, $T: typeid) -> (res: [N]T) {
// `N` is the constant value passed
// `I` is the type of N
// `T` is the type passed
fmt.printf("Generating an array of type %v from the value %v of type %v\n",
typeid_of(type_of(res)), N, typeid_of(I));
for i in 0..<N {
res[i] = i*i;
}
return;
}
T :: int;
array := foo(4, T);
for v, i in array {
assert(v == T(i*i));
}
In some cases, you may want to specify that a type must be a specialization of a certain type.
// Only allow types that are specializations of a (polymorphic) slice
make_slice :: proc($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) {
...
}
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:
simple_sanity_check :: proc(x: [2]int)
where len(x) > 1,
type_of(x) == [2]int {
fmt.println(x);
}
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.z;
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));
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);
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));
The following are useful idioms which are emergent from the semantics on the language.
if str, ok := value.(string); ok {
...
} else {
...
}
Foo :: struct {
f: float,
i: int,
}
foos := make([]Foo, num);
// By-value basic ranged-based loop, with implicit indexing
for v, j in foos {
using v;
fmt.println(i, 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);
}
defer if cond {
}
Subtype polymorphism with runtime type safe down casting:
Entity :: struct {
id: u64,
name: string,
derived: any,
}
Frog :: struct {
using entity: Entity,
volume: f32,
jump_height: i32,
}
new_entity :: proc($T: typeid) -> ^T {
e := new(T);
e.derived = e^;
return e;
}
entity: ^Entity = new_entity(Frog);
switch e in entity.derived {
case Frog:
fmt.println("Ribbit:", e.volume);
}
More details can be found on the Github wiki for Odin[10]. Some of this information includes:
10: https://github.com/odin-lang/Odin/wiki