Zig Language Reference

const std = @import("std");

pub fn main() !void {
    const stdout = std.io.getStdOut().writer();
    try stdout.print("Hello, {s}!\n", .{"world"});
}

$ zig build-exe hello.zig
$ ./hello
Hello, world!

const print = @import("std").debug.print;

pub fn main() void {
    print("Hello, world!\n", .{});
}

$ zig build-exe hello_again.zig
$ ./hello_again
Hello, world!

zig test -femit-docs main.zig

const print = @import("std").debug.print;

pub fn main() void {
    // Comments in Zig start with "//" and end at the next LF byte (end of line).
    // The line below is a comment and won't be executed.

    //print("Hello?", .{});

    print("Hello, world!\n", .{}); // another comment
}

$ zig build-exe comments.zig
$ ./comments
Hello, world!

/// A structure for storing a timestamp, with nanosecond precision (this is a
/// multiline doc comment).
const Timestamp = struct {
    /// The number of seconds since the epoch (this is also a doc comment).
    seconds: i64,  // signed so we can represent pre-1970 (not a doc comment)
    /// The number of nanoseconds past the second (doc comment again).
    nanos: u32,

    /// Returns a `Timestamp` struct representing the Unix epoch; that is, the
    /// moment of 1970 Jan 1 00:00:00 UTC (this is a doc comment too).
    pub fn unixEpoch() Timestamp {
        return Timestamp{
            .seconds = 0,
            .nanos = 0,
        };
    }
};

/// doc-comment
//! top-level doc-comment
const std = @import("std");

$ zig build-obj invalid_doc-comment.zig
docgen_tmp/invalid_doc-comment.zig:1:16: error: expected type expression, found 'a document comment'
/// doc-comment
               ^

pub fn main() void {}

/// End of file

$ zig build-obj unattached_doc-comment.zig
docgen_tmp/unattached_doc-comment.zig:3:1: error: unattached documentation comment
/// End of file
^~~~~~~~~~~~~~~

//! This module provides functions for retrieving the current date and
//! time with varying degrees of precision and accuracy. It does not
//! depend on libc, but will use functions from it if available.

const S = struct {
    //! Top level comments are allowed inside a container other than a module,
    //! but it is not very useful.  Currently, when producing the package
    //! documentation, these comments are ignored.
};

// Top-level declarations are order-independent:
const print = std.debug.print;
const std = @import("std");
const os = std.os;
const assert = std.debug.assert;

pub fn main() void {
    // integers
    const one_plus_one: i32 = 1 + 1;
    print("1 + 1 = {}\n", .{one_plus_one});

    // floats
    const seven_div_three: f32 = 7.0 / 3.0;
    print("7.0 / 3.0 = {}\n", .{seven_div_three});

    // boolean
    print("{}\n{}\n{}\n", .{
        true and false,
        true or false,
        !true,
    });

    // optional
    var optional_value: ?[]const u8 = null;
    assert(optional_value == null);

    print("\noptional 1\ntype: {}\nvalue: {?s}\n", .{
        @TypeOf(optional_value), optional_value,
    });

    optional_value = "hi";
    assert(optional_value != null);

    print("\noptional 2\ntype: {}\nvalue: {?s}\n", .{
        @TypeOf(optional_value), optional_value,
    });

    // error union
    var number_or_error: anyerror!i32 = error.ArgNotFound;

    print("\nerror union 1\ntype: {}\nvalue: {!}\n", .{
        @TypeOf(number_or_error), number_or_error, });

    number_or_error = 1234;

    print("\nerror union 2\ntype: {}\nvalue: {!}\n", .{
        @TypeOf(number_or_error), number_or_error,
    });
}

$ zig build-exe values.zig
$ ./values
1 + 1 = 2
7.0 / 3.0 = 2.33333325e+00
false
true
false

optional 1
type: ?[]const u8
value: null

optional 2
type: ?[]const u8
value: hi

error union 1
type: anyerror!i32
value: error.ArgNotFound

error union 2
type: anyerror!i32
value: 1234

const print = @import("std").debug.print;
const mem = @import("std").mem; // will be used to compare bytes

pub fn main() void {
    const bytes = "hello";
    print("{}\n", .{@TypeOf(bytes)});                   // *const [5:0]u8
    print("{d}\n", .{bytes.len});                       // 5
    print("{c}\n", .{bytes[1]});                        // 'e'
    print("{d}\n", .{bytes[5]});                        // 0
    print("{}\n", .{'e' == '\x65'});                    // true
    print("{d}\n", .{'\u{1f4a9}'});                     // 128169
    print("{d}\n", .{'💯'});                            // 128175
    print("{u}\n", .{'⚡'});
    print("{}\n", .{mem.eql(u8, "hello", "h\x65llo")});      // true
    print("{}\n", .{mem.eql(u8, "💯", "\xf0\x9f\x92\xaf")}); // also true
    const invalid_utf8 = "\xff\xfe";      // non-UTF-8 strings are possible with \xNN notation.
    print("0x{x}\n", .{invalid_utf8[1]}); // indexing them returns individual bytes...
    print("0x{x}\n", .{"💯"[1]});    // ...as does indexing part-way through non-ASCII characters
}

$ zig build-exe string_literals.zig
$ ./string_literals
*const [5:0]u8
5
e
0
true
128169
128175
⚡
true
true
0xfe
0x9f

const hello_world_in_c =
    \\#include <stdio.h>
    \\
    \\int main(int argc, char **argv) {
    \\    printf("hello world\n");
    \\    return 0;
    \\}
;

const x = 1234;

fn foo() void {
    // It works at file scope as well as inside functions.
    const y = 5678;

    // Once assigned, an identifier cannot be changed.
    y += 1;
}

pub fn main() void {
    foo();
}

$ zig build-exe constant_identifier_cannot_change.zig
constant_identifier_cannot_change.zig:8:7: error: cannot assign to constant
    y += 1;
    ~~^~~~
referenced by:
    main: constant_identifier_cannot_change.zig:12:5
    callMain: /builddir/build/BUILD/zig-0.11.0/redhat-linux-build/stage3/lib/zig/std/start.zig:564:17
    remaining reference traces hidden; use '-freference-trace' to see all reference traces

const print = @import("std").debug.print;

pub fn main() void {
    var y: i32 = 5678;

    y += 1;

    print("{d}", .{y});
}

$ zig build-exe mutable_var.zig
$ ./mutable_var
5679

pub fn main() void {
    var x: i32;

    x = 1;
}

$ zig build-exe var_must_be_initialized.zig
var_must_be_initialized.zig:2:5: error: variables must be initialized
    var x: i32;
    ^~~~~~~~~~

const print = @import("std").debug.print;

pub fn main() void {
    var x: i32 = undefined;
    x = 1;
    print("{d}", .{x});
}

$ zig build-exe assign_undefined.zig
$ ./assign_undefined
1

const std = @import("std");

test "expect addOne adds one to 41" {

    // The Standard Library contains useful functions to help create tests.
    // `expect` is a function that verifies its argument is true.
    // It will return an error if its argument is false to indicate a failure.
    // `try` is used to return an error to the test runner to notify it that the test failed.
    try std.testing.expect(addOne(41) == 42);
}

test addOne {
    // A test name can also be written using an identifier.
    try std.testing.expect(addOne(41) == 42);
}

/// The function `addOne` adds one to the number given as its argument.
fn addOne(number: i32) i32 {
    return number + 1;
}

$ zig test testing_introduction.zig
1/2 test.expect addOne adds one to 41... OK
2/2 decltest.addOne... OK
All 2 tests passed.

const std = @import("std");
const expect = std.testing.expect;

// Imported source file tests will run when referenced from a top-level test declaration.
// The next line alone does not cause "testing_introduction.zig" tests to run.
const imported_file = @import("testing_introduction.zig");

test {
    // To run nested container tests, either, call `refAllDecls` which will
    // reference all declarations located in the given argument.
    // `@This()` is a builtin function that returns the innermost container it is called from.
    // In this example, the innermost container is this file (implicitly a struct).
    std.testing.refAllDecls(@This());

    // or, reference each container individually from a top-level test declaration.
    // The `_ = C;` syntax is a no-op reference to the identifier `C`.
    _ = S;
    _ = U;
    _ = @import("testing_introduction.zig");
}

const S = struct {
    test "S demo test" {
        try expect(true);
    }

    const SE = enum {
        V,

        // This test won't run because its container (SE) is not referenced.
        test "This Test Won't Run" {
            try expect(false);
        }
    };
};

const U = union { // U is referenced by the file's top-level test declaration
    s: US,        // and US is referenced here; therefore, "U.Us demo test" will run

    const US = struct {
        test "U.US demo test" {
            // This test is a top-level test declaration for the struct.
            // The struct is nested (declared) inside of a union.
            try expect(true);
        }
    };

    test "U demo test" {
        try expect(true);
    }
};

$ zig test testing_nested_container_tests.zig
1/5 test_0... OK
2/5 test.S demo test... OK
3/5 test.U demo test... OK
4/5 test.expect addOne adds one to 41... OK
5/5 decltest.addOne... OK
All 5 tests passed.

const std = @import("std");

test "expect this to fail" {
    try std.testing.expect(false);
}

test "expect this to succeed" {
    try std.testing.expect(true);
}

$ zig test testing_failure.zig
1/2 test.expect this to fail... FAIL (TestUnexpectedResult)
/builddir/build/BUILD/zig-0.11.0/redhat-linux-build/stage3/lib/zig/std/testing.zig:515:14: 0x22431f in expect (test)
    if (!ok) return error.TestUnexpectedResult;
             ^
/builddir/build/BUILD/zig-0.11.0/docgen_tmp/testing_failure.zig:4:5: 0x224435 in test.expect this to fail (test)
    try std.testing.expect(false);
    ^
2/2 test.expect this to succeed... OK
1 passed; 0 skipped; 1 failed.
error: the following test command failed with exit code 1:
/builddir/build/BUILD/zig-0.11.0/zig-cache/o/ea34a50ec938606cdb2fbd416797a9a3/test

test "this will be skipped" {
    return error.SkipZigTest;
}

$ zig test testing_skip.zig
1/1 test.this will be skipped... SKIP
0 passed; 1 skipped; 0 failed.

const std = @import("std");

test "detect leak" {
    var list = std.ArrayList(u21).init(std.testing.allocator);
    // missing `defer list.deinit();`
    try list.append('☔');

    try std.testing.expect(list.items.len == 1);
}

$ zig test testing_detect_leak.zig
1/1 test.detect leak... OK
[gpa] (err): memory address 0x7f1cb7977000 leaked:
/builddir/build/BUILD/zig-0.11.0/redhat-linux-build/stage3/lib/zig/std/array_list.zig:403:67: 0x234dce in ensureTotalCapacityPrecise (test)
                const new_memory = try self.allocator.alignedAlloc(T, alignment, new_capacity);
                                                                  ^
/builddir/build/BUILD/zig-0.11.0/redhat-linux-build/stage3/lib/zig/std/array_list.zig:379:51: 0x22b1e4 in ensureTotalCapacity (test)
            return self.ensureTotalCapacityPrecise(better_capacity);
                                                  ^
/builddir/build/BUILD/zig-0.11.0/redhat-linux-build/stage3/lib/zig/std/array_list.zig:426:41: 0x228990 in addOne (test)
            try self.ensureTotalCapacity(self.items.len + 1);
                                        ^
/builddir/build/BUILD/zig-0.11.0/redhat-linux-build/stage3/lib/zig/std/array_list.zig:207:49: 0x22473b in append (test)
            const new_item_ptr = try self.addOne();
                                                ^
/builddir/build/BUILD/zig-0.11.0/docgen_tmp/testing_detect_leak.zig:6:20: 0x224662 in test.detect leak (test)
    try list.append('☔');
                   ^
/builddir/build/BUILD/zig-0.11.0/redhat-linux-build/stage3/lib/zig/test_runner.zig:176:28: 0x232405 in mainTerminal (test)
        } else test_fn.func();
                           ^
/builddir/build/BUILD/zig-0.11.0/redhat-linux-build/stage3/lib/zig/test_runner.zig:36:28: 0x22927a in main (test)
        return mainTerminal();
                           ^
/builddir/build/BUILD/zig-0.11.0/redhat-linux-build/stage3/lib/zig/std/start.zig:564:22: 0x224c42 in posixCallMainAndExit (test)
            root.main();
                     ^

All 1 tests passed.
1 errors were logged.
1 tests leaked memory.
error: the following test command failed with exit code 1:
/builddir/build/BUILD/zig-0.11.0/zig-cache/o/d1d47ee2c9512db6c178967b527d0106/test

const std = @import("std");
const builtin = @import("builtin");
const expect = std.testing.expect;

test "builtin.is_test" {
    try expect(isATest());
}

fn isATest() bool {
    return builtin.is_test;
}

$ zig test testing_detect_test.zig
1/1 test.builtin.is_test... OK
All 1 tests passed.

const std = @import("std");

test "expectEqual demo" {
    const expected: i32 = 42;
    const actual = 42;

    // The first argument to `expectEqual` is the known, expected, result.
    // The second argument is the result of some expression.
    // The actual's type is casted to the type of expected.
    try std.testing.expectEqual(expected, actual);
}

test "expectError demo" {
    const expected_error = error.DemoError;
    const actual_error_union: anyerror!void = error.DemoError;

    // `expectError` will fail when the actual error is different than
    // the expected error.
    try std.testing.expectError(expected_error, actual_error_union);
}

$ zig test testing_namespace.zig
1/2 test.expectEqual demo... OK
2/2 test.expectError demo... OK
All 2 tests passed.

const @"identifier with spaces in it" = 0xff;
const @"1SmallStep4Man" = 112358;

const c = @import("std").c;
pub extern "c" fn @"error"() void;
pub extern "c" fn @"fstat$INODE64"(fd: c.fd_t, buf: *c.Stat) c_int;

const Color = enum {
  red,
  @"really red",
};
const color: Color = .@"really red";

var y: i32 = add(10, x);
const x: i32 = add(12, 34);

test "container level variables" {
    try expect(x == 46);
    try expect(y == 56);
}

fn add(a: i32, b: i32) i32 {
    return a + b;
}

const std = @import("std");
const expect = std.testing.expect;

$ zig test test_container_level_variables.zig
1/1 test.container level variables... OK
All 1 tests passed.

const std = @import("std");
const expect = std.testing.expect;

test "namespaced container level variable" {
    try expect(foo() == 1235);
    try expect(foo() == 1236);
}

const S = struct {
    var x: i32 = 1234;
};

fn foo() i32 {
    S.x += 1;
    return S.x;
}

$ zig test test_namespaced_container_level_variable.zig
1/1 test.namespaced container level variable... OK
All 1 tests passed.

const std = @import("std");
const expect = std.testing.expect;

test "static local variable" {
    try expect(foo() == 1235);
    try expect(foo() == 1236);
}

fn foo() i32 {
    const S = struct {
        var x: i32 = 1234;
    };
    S.x += 1;
    return S.x;
}

$ zig test test_static_local_variable.zig
1/1 test.static local variable... OK
All 1 tests passed.

const std = @import("std");
const assert = std.debug.assert;

threadlocal var x: i32 = 1234;

test "thread local storage" {
    const thread1 = try std.Thread.spawn(.{}, testTls, .{});
    const thread2 = try std.Thread.spawn(.{}, testTls, .{});
    testTls();
    thread1.join();
    thread2.join();
}

fn testTls() void {
    assert(x == 1234);
    x += 1;
    assert(x == 1235);
}

$ zig test test_thread_local_variables.zig
1/1 test.thread local storage... OK
All 1 tests passed.

const std = @import("std");
const expect = std.testing.expect;

test "comptime vars" {
    var x: i32 = 1;
    comptime var y: i32 = 1;

    x += 1;
    y += 1;

    try expect(x == 2);
    try expect(y == 2);

    if (y != 2) {
        // This compile error never triggers because y is a comptime variable,
        // and so `y != 2` is a comptime value, and this if is statically evaluated.
        @compileError("wrong y value");
    }
}

$ zig test test_comptime_variables.zig
1/1 test.comptime vars... OK
All 1 tests passed.

const decimal_int = 98222;
const hex_int = 0xff;
const another_hex_int = 0xFF;
const octal_int = 0o755;
const binary_int = 0b11110000;

// underscores may be placed between two digits as a visual separator
const one_billion = 1_000_000_000;
const binary_mask = 0b1_1111_1111;
const permissions = 0o7_5_5;
const big_address = 0xFF80_0000_0000_0000;

fn divide(a: i32, b: i32) i32 {
    return a / b;
}

const floating_point = 123.0E+77;
const another_float = 123.0;
const yet_another = 123.0e+77;

const hex_floating_point = 0x103.70p-5;
const another_hex_float = 0x103.70;
const yet_another_hex_float = 0x103.70P-5;

// underscores may be placed between two digits as a visual separator
const lightspeed = 299_792_458.000_000;
const nanosecond = 0.000_000_001;
const more_hex = 0x1234_5678.9ABC_CDEFp-10;

const std = @import("std");

const inf = std.math.inf(f32);
const negative_inf = -std.math.inf(f64);
const nan = std.math.nan(f128);

const std = @import("std");
const big = @as(f64, 1 << 40);

export fn foo_strict(x: f64) f64 {
    return x + big - big;
}

export fn foo_optimized(x: f64) f64 {
    @setFloatMode(.Optimized);
    return x + big - big;
}

$ zig build-obj float_mode_obj.zig -O ReleaseFast

const print = @import("std").debug.print;

extern fn foo_strict(x: f64) f64;
extern fn foo_optimized(x: f64) f64;

pub fn main() void {
    const x = 0.001;
    print("optimized = {}\n", .{foo_optimized(x)});
    print("strict = {}\n", .{foo_strict(x)});
}

$ zig build-exe float_mode_exe.zig float_mode_obj.o
$ ./float_mode_exe
optimized = 9.765625e-04
strict = 9.765625e-04

const expect = @import("std").testing.expect;
const assert = @import("std").debug.assert;
const mem = @import("std").mem;

// array literal
const message = [_]u8{ 'h', 'e', 'l', 'l', 'o' };

// get the size of an array
comptime {
    assert(message.len == 5);
}

// A string literal is a single-item pointer to an array.
const same_message = "hello";

comptime {
    assert(mem.eql(u8, &message, same_message));
}

test "iterate over an array" {
    var sum: usize = 0;
    for (message) |byte| {
        sum += byte;
    }
    try expect(sum == 'h' + 'e' + 'l' * 2 + 'o');
}

// modifiable array
var some_integers: [100]i32 = undefined;

test "modify an array" {
    for (&some_integers, 0..) |*item, i| {
        item.* = @intCast(i);
    }
    try expect(some_integers[10] == 10);
    try expect(some_integers[99] == 99);
}

// array concatenation works if the values are known
// at compile time
const part_one = [_]i32{ 1, 2, 3, 4 };
const part_two = [_]i32{ 5, 6, 7, 8 };
const all_of_it = part_one ++ part_two;
comptime {
    assert(mem.eql(i32, &all_of_it, &[_]i32{ 1, 2, 3, 4, 5, 6, 7, 8 }));
}

// remember that string literals are arrays
const hello = "hello";
const world = "world";
const hello_world = hello ++ " " ++ world;
comptime {
    assert(mem.eql(u8, hello_world, "hello world"));
}

// ** does repeating patterns
const pattern = "ab" ** 3;
comptime {
    assert(mem.eql(u8, pattern, "ababab"));
}

// initialize an array to zero
const all_zero = [_]u16{0} ** 10;

comptime {
    assert(all_zero.len == 10);
    assert(all_zero[5] == 0);
}

// use compile-time code to initialize an array
var fancy_array = init: {
    var initial_value: [10]Point = undefined;
    for (&initial_value, 0..) |*pt, i| {
        pt.* = Point{
            .x = @intCast(i),
            .y = @intCast(i * 2),
        };
    }
    break :init initial_value;
};
const Point = struct {
    x: i32,
    y: i32,
};

test "compile-time array initialization" {
    try expect(fancy_array[4].x == 4);
    try expect(fancy_array[4].y == 8);
}

// call a function to initialize an array
var more_points = [_]Point{makePoint(3)} ** 10;
fn makePoint(x: i32) Point {
    return Point{
        .x = x,
        .y = x * 2,
    };
}
test "array initialization with function calls" {
    try expect(more_points[4].x == 3);
    try expect(more_points[4].y == 6);
    try expect(more_points.len == 10);
}

$ zig test test_arrays.zig
1/4 test.iterate over an array... OK
2/4 test.modify an array... OK
3/4 test.compile-time array initialization... OK
4/4 test.array initialization with function calls... OK
All 4 tests passed.

const std = @import("std");
const expect = std.testing.expect;

const mat4x4 = [4][4]f32{
    [_]f32{ 1.0, 0.0, 0.0, 0.0 },
    [_]f32{ 0.0, 1.0, 0.0, 1.0 },
    [_]f32{ 0.0, 0.0, 1.0, 0.0 },
    [_]f32{ 0.0, 0.0, 0.0, 1.0 },
};
test "multidimensional arrays" {
    // Access the 2D array by indexing the outer array, and then the inner array.
    try expect(mat4x4[1][1] == 1.0);

    // Here we iterate with for loops.
    for (mat4x4, 0..) |row, row_index| {
        for (row, 0..) |cell, column_index| {
            if (row_index == column_index) {
                try expect(cell == 1.0);
            }
        }
    }
}

$ zig test test_multidimensional_arrays.zig
1/1 test.multidimensional arrays... OK
All 1 tests passed.

const std = @import("std");
const expect = std.testing.expect;

test "null terminated array" {
    const array = [_:0]u8 {1, 2, 3, 4};

    try expect(@TypeOf(array) == [4:0]u8);
    try expect(array.len == 4);
    try expect(array[4] == 0);
}

$ zig test test_null_terminated_array.zig
1/1 test.null terminated array... OK
All 1 tests passed.

const std = @import("std");
const expectEqual = std.testing.expectEqual;

test "Basic vector usage" {
    // Vectors have a compile-time known length and base type.
    const a = @Vector(4, i32){ 1, 2, 3, 4 };
    const b = @Vector(4, i32){ 5, 6, 7, 8 };

    // Math operations take place element-wise.
    const c = a + b;

    // Individual vector elements can be accessed using array indexing syntax.
    try expectEqual(6, c[0]);
    try expectEqual(8, c[1]);
    try expectEqual(10, c[2]);
    try expectEqual(12, c[3]);
}

test "Conversion between vectors, arrays, and slices" {
    // Vectors and fixed-length arrays can be automatically assigned back and forth
    var arr1: [4]f32 = [_]f32{ 1.1, 3.2, 4.5, 5.6 };
    var vec: @Vector(4, f32) = arr1;
    var arr2: [4]f32 = vec;
    try expectEqual(arr1, arr2);

    // You can also assign from a slice with comptime-known length to a vector using .*
    const vec2: @Vector(2, f32) = arr1[1..3].*;

    var slice: []const f32 = &arr1;
    var offset: u32 = 1;
    // To extract a comptime-known length from a runtime-known offset,
    // first extract a new slice from the starting offset, then an array of
    // comptime-known length
    const vec3: @Vector(2, f32) = slice[offset..][0..2].*;
    try expectEqual(slice[offset], vec2[0]);
    try expectEqual(slice[offset + 1], vec2[1]);
    try expectEqual(vec2, vec3);
}

$ zig test test_vector.zig
1/2 test.Basic vector usage... OK
2/2 test.Conversion between vectors, arrays, and slices... OK
All 2 tests passed.

const expect = @import("std").testing.expect;

test "address of syntax" {
    // Get the address of a variable:
    const x: i32 = 1234;
    const x_ptr = &x;

    // Dereference a pointer:
    try expect(x_ptr.* == 1234);

    // When you get the address of a const variable, you get a const single-item pointer.
    try expect(@TypeOf(x_ptr) == *const i32);

    // If you want to mutate the value, you'd need an address of a mutable variable:
    var y: i32 = 5678;
    const y_ptr = &y;
    try expect(@TypeOf(y_ptr) == *i32);
    y_ptr.* += 1;
    try expect(y_ptr.* == 5679);
}

test "pointer array access" {
    // Taking an address of an individual element gives a
    // single-item pointer. This kind of pointer
    // does not support pointer arithmetic.
    var array = [_]u8{ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
    const ptr = &array[2];
    try expect(@TypeOf(ptr) == *u8);

    try expect(array[2] == 3);
    ptr.* += 1;
    try expect(array[2] == 4);
}

$ zig test test_single_item_pointer.zig
1/2 test.address of syntax... OK
2/2 test.pointer array access... OK
All 2 tests passed.

const expect = @import("std").testing.expect;

test "pointer arithmetic with many-item pointer" {
    const array = [_]i32{ 1, 2, 3, 4 };
    var ptr: [*]const i32 = &array;

    try expect(ptr[0] == 1);
    ptr += 1;
    try expect(ptr[0] == 2);
}

test "pointer arithmetic with slices" {
    var array = [_]i32{ 1, 2, 3, 4 };
    var length: usize = 0;
    var slice = array[length..array.len];

    try expect(slice[0] == 1);
    try expect(slice.len == 4);

    slice.ptr += 1;
    // now the slice is in an bad state since len has not been updated

    try expect(slice[0] == 2);
    try expect(slice.len == 4);
}

$ zig test test_pointer_arithmetic.zig
1/2 test.pointer arithmetic with many-item pointer... OK
2/2 test.pointer arithmetic with slices... OK
All 2 tests passed.

const expect = @import("std").testing.expect;

test "pointer slicing" {
    var array = [_]u8{ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
    var start: usize = 2;
    const slice = array[start..4];
    try expect(slice.len == 2);

    try expect(array[3] == 4);
    slice[1] += 1;
    try expect(array[3] == 5);
}

$ zig test test_slice_bounds.zig
1/1 test.pointer slicing... OK
All 1 tests passed.

const expect = @import("std").testing.expect;

test "comptime pointers" {
    comptime {
        var x: i32 = 1;
        const ptr = &x;
        ptr.* += 1;
        x += 1;
        try expect(ptr.* == 3);
    }
}

$ zig test test_comptime_pointers.zig
1/1 test.comptime pointers... OK
All 1 tests passed.

const expect = @import("std").testing.expect;

test "@intFromPtr and @ptrFromInt" {
    const ptr: *i32 = @ptrFromInt(0xdeadbee0);
    const addr = @intFromPtr(ptr);
    try expect(@TypeOf(addr) == usize);
    try expect(addr == 0xdeadbee0);
}

$ zig test test_integer_pointer_conversion.zig
1/1 test.@intFromPtr and @ptrFromInt... OK
All 1 tests passed.

const expect = @import("std").testing.expect;

test "comptime @ptrFromInt" {
    comptime {
        // Zig is able to do this at compile-time, as long as
        // ptr is never dereferenced.
        const ptr: *i32 = @ptrFromInt(0xdeadbee0);
        const addr = @intFromPtr(ptr);
        try expect(@TypeOf(addr) == usize);
        try expect(addr == 0xdeadbee0);
    }
}

$ zig test test_comptime_pointer_conversion.zig
1/1 test.comptime @ptrFromInt... OK
All 1 tests passed.

const expect = @import("std").testing.expect;

test "volatile" {
    const mmio_ptr: *volatile u8 = @ptrFromInt(0x12345678);
    try expect(@TypeOf(mmio_ptr) == *volatile u8);
}

$ zig test test_volatile.zig
1/1 test.volatile... OK
All 1 tests passed.

const std = @import("std");
const expect = std.testing.expect;

test "pointer casting" {
    const bytes align(@alignOf(u32)) = [_]u8{ 0x12, 0x12, 0x12, 0x12 };
    const u32_ptr: *const u32 = @ptrCast(&bytes);
    try expect(u32_ptr.* == 0x12121212);

    // Even this example is contrived - there are better ways to do the above than
    // pointer casting. For example, using a slice narrowing cast:
    const u32_value = std.mem.bytesAsSlice(u32, bytes[0..])[0];
    try expect(u32_value == 0x12121212);

    // And even another way, the most straightforward way to do it:
    try expect(@as(u32, @bitCast(bytes)) == 0x12121212);
}

test "pointer child type" {
    // pointer types have a `child` field which tells you the type they point to.
    try expect(@typeInfo(*u32).Pointer.child == u32);
}

$ zig test test_pointer_casting.zig
1/2 test.pointer casting... OK
2/2 test.pointer child type... OK
All 2 tests passed.

const std = @import("std");
const builtin = @import("builtin");
const expect = std.testing.expect;

test "variable alignment" {
    var x: i32 = 1234;
    const align_of_i32 = @alignOf(@TypeOf(x));
    try expect(@TypeOf(&x) == *i32);
    try expect(*i32 == *align(align_of_i32) i32);
    if (builtin.target.cpu.arch == .x86_64) {
        try expect(@typeInfo(*i32).Pointer.alignment == 4);
    }
}

$ zig test test_variable_alignment.zig
1/1 test.variable alignment... OK
All 1 tests passed.

const expect = @import("std").testing.expect;

var foo: u8 align(4) = 100;

test "global variable alignment" {
    try expect(@typeInfo(@TypeOf(&foo)).Pointer.alignment == 4);
    try expect(@TypeOf(&foo) == *align(4) u8);
    const as_pointer_to_array: *align(4) [1]u8 = &foo;
    const as_slice: []align(4) u8 = as_pointer_to_array;
    const as_unaligned_slice: []u8 = as_slice;
    try expect(as_unaligned_slice[0] == 100);
}

fn derp() align(@sizeOf(usize) * 2) i32 {
    return 1234;
}
fn noop1() align(1) void {}
fn noop4() align(4) void {}

test "function alignment" {
    try expect(derp() == 1234);
    try expect(@TypeOf(noop1) == fn () align(1) void);
    try expect(@TypeOf(noop4) == fn () align(4) void);
    noop1();
    noop4();
}

$ zig test test_variable_func_alignment.zig
1/2 test.global variable alignment... OK
2/2 test.function alignment... OK
All 2 tests passed.

const std = @import("std");

test "pointer alignment safety" {
    var array align(4) = [_]u32{ 0x11111111, 0x11111111 };
    const bytes = std.mem.sliceAsBytes(array[0..]);
    try std.testing.expect(foo(bytes) == 0x11111111);
}
fn foo(bytes: []u8) u32 {
    const slice4 = bytes[1..5];
    const int_slice = std.mem.bytesAsSlice(u32, @as([]align(4) u8, @alignCast(slice4)));
    return int_slice[0];
}

$ zig test test_incorrect_pointer_alignment.zig
1/1 test.pointer alignment safety... thread 799 panic: incorrect alignment
/builddir/build/BUILD/zig-0.11.0/docgen_tmp/test_incorrect_pointer_alignment.zig:10:68: 0x22459f in foo (test)
    const int_slice = std.mem.bytesAsSlice(u32, @as([]align(4) u8, @alignCast(slice4)));
                                                                   ^
/builddir/build/BUILD/zig-0.11.0/docgen_tmp/test_incorrect_pointer_alignment.zig:6:31: 0x22448f in test.pointer alignment safety (test)
    try std.testing.expect(foo(bytes) == 0x11111111);
                              ^
/builddir/build/BUILD/zig-0.11.0/redhat-linux-build/stage3/lib/zig/test_runner.zig:176:28: 0x22d275 in mainTerminal (test)
        } else test_fn.func();
                           ^
/builddir/build/BUILD/zig-0.11.0/redhat-linux-build/stage3/lib/zig/test_runner.zig:36:28: 0x2254ea in main (test)
        return mainTerminal();
                           ^
/builddir/build/BUILD/zig-0.11.0/redhat-linux-build/stage3/lib/zig/std/start.zig:564:22: 0x224a82 in posixCallMainAndExit (test)
            root.main();
                     ^
/builddir/build/BUILD/zig-0.11.0/redhat-linux-build/stage3/lib/zig/std/start.zig:243:5: 0x2245d1 in _start (test)
    asm volatile (switch (native_arch) {
    ^
???:?:?: 0x0 in ??? (???)
error: the following test command crashed:
/builddir/build/BUILD/zig-0.11.0/zig-cache/o/4c71750281b04debae78a960d6c4ef14/test

const std = @import("std");
const expect = std.testing.expect;

test "allowzero" {
    var zero: usize = 0;
    var ptr: *allowzero i32 = @ptrFromInt(zero);
    try expect(@intFromPtr(ptr) == 0);
}

$ zig test test_allowzero.zig
1/1 test.allowzero... OK
All 1 tests passed.

const std = @import("std");

// This is also available as `std.c.printf`.
pub extern "c" fn printf(format: [*:0]const u8, ...) c_int;

pub fn main() anyerror!void {
    _ = printf("Hello, world!\n"); // OK

    const msg = "Hello, world!\n";
    const non_null_terminated_msg: [msg.len]u8 = msg.*;
    _ = printf(&non_null_terminated_msg);
}

$ zig build-exe sentinel-terminated_pointer.zig -lc
sentinel-terminated_pointer.zig:11:16: error: expected type '[*:0]const u8', found '*const [14]u8'
    _ = printf(&non_null_terminated_msg);
               ^~~~~~~~~~~~~~~~~~~~~~~~
sentinel-terminated_pointer.zig:11:16: note: destination pointer requires '0' sentinel
sentinel-terminated_pointer.zig:4:35: note: parameter type declared here
pub extern "c" fn printf(format: [*:0]const u8, ...) c_int;
                                 ~^~~~~~~~~~~~
referenced by:
    callMain: /builddir/build/BUILD/zig-0.11.0/redhat-linux-build/stage3/lib/zig/std/start.zig:574:32
    initEventLoopAndCallMain: /builddir/build/BUILD/zig-0.11.0/redhat-linux-build/stage3/lib/zig/std/start.zig:508:34
    remaining reference traces hidden; use '-freference-trace' to see all reference traces

const expect = @import("std").testing.expect;

test "basic slices" {
    var array = [_]i32{ 1, 2, 3, 4 };
    // A slice is a pointer and a length. The difference between an array and
    // a slice is that the array's length is part of the type and known at
    // compile-time, whereas the slice's length is known at runtime.
    // Both can be accessed with the `len` field.
    var known_at_runtime_zero: usize = 0;
    const slice = array[known_at_runtime_zero..array.len];
    try expect(@TypeOf(slice) == []i32);
    try expect(&slice[0] == &array[0]);
    try expect(slice.len == array.len);

    // If you slice with comptime-known start and end positions, the result is
    // a pointer to an array, rather than a slice.
    const array_ptr = array[0..array.len];
    try expect(@TypeOf(array_ptr) == *[array.len]i32);

    // You can perform a slice-by-length by slicing twice. This allows the compiler
    // to perform some optimisations like recognising a comptime-known length when
    // the start position is only known at runtime.
    var runtime_start: usize = 1;
    const length = 2;
    const array_ptr_len = array[runtime_start..][0..length];
    try expect(@TypeOf(array_ptr_len) == *[length]i32);

    // Using the address-of operator on a slice gives a single-item pointer,
    // while using the `ptr` field gives a many-item pointer.
    try expect(@TypeOf(slice.ptr) == [*]i32);
    try expect(@TypeOf(&slice[0]) == *i32);
    try expect(@intFromPtr(slice.ptr) == @intFromPtr(&slice[0]));

    // Slices have array bounds checking. If you try to access something out
    // of bounds, you'll get a safety check failure:
    slice[10] += 1;

    // Note that `slice.ptr` does not invoke safety checking, while `&slice[0]`
    // asserts that the slice has len > 0.
}

$ zig test test_basic_slices.zig
1/1 test.basic slices... thread 829 panic: index out of bounds: index 10, len 4
/builddir/build/BUILD/zig-0.11.0/docgen_tmp/test_basic_slices.zig:36:10: 0x224765 in test.basic slices (test)
    slice[10] += 1;
         ^
/builddir/build/BUILD/zig-0.11.0/redhat-linux-build/stage3/lib/zig/test_runner.zig:176:28: 0x22db25 in mainTerminal (test)
        } else test_fn.func();
                           ^
/builddir/build/BUILD/zig-0.11.0/redhat-linux-build/stage3/lib/zig/test_runner.zig:36:28: 0x225cca in main (test)
        return mainTerminal();
                           ^
/builddir/build/BUILD/zig-0.11.0/redhat-linux-build/stage3/lib/zig/std/start.zig:564:22: 0x224d62 in posixCallMainAndExit (test)
            root.main();
                     ^
/builddir/build/BUILD/zig-0.11.0/redhat-linux-build/stage3/lib/zig/std/start.zig:243:5: 0x2248b1 in _start (test)
    asm volatile (switch (native_arch) {
    ^
???:?:?: 0x0 in ??? (???)
error: the following test command crashed:
/builddir/build/BUILD/zig-0.11.0/zig-cache/o/336cf9237a992d21e3bf8011f350213f/test

const std = @import("std");
const expect = std.testing.expect;
const mem = std.mem;
const fmt = std.fmt;

test "using slices for strings" {
    // Zig has no concept of strings. String literals are const pointers
    // to null-terminated arrays of u8, and by convention parameters
    // that are "strings" are expected to be UTF-8 encoded slices of u8.
    // Here we coerce *const [5:0]u8 and *const [6:0]u8 to []const u8
    const hello: []const u8 = "hello";
    const world: []const u8 = "世界";

    var all_together: [100]u8 = undefined;
    // You can use slice syntax with at least one runtime-known index on an
    // array to convert an array into a slice.
    var start : usize = 0;
    const all_together_slice = all_together[start..];
    // String concatenation example.
    const hello_world = try fmt.bufPrint(all_together_slice, "{s} {s}", .{ hello, world });

    // Generally, you can use UTF-8 and not worry about whether something is a
    // string. If you don't need to deal with individual characters, no need
    // to decode.
    try expect(mem.eql(u8, hello_world, "hello 世界"));
}

test "slice pointer" {
    var a: []u8 = undefined;
    try expect(@TypeOf(a) == []u8);
    var array: [10]u8 = undefined;
    const ptr = &array;
    try expect(@TypeOf(ptr) == *[10]u8);

    // A pointer to an array can be sliced just like an array:
    var start: usize = 0;
    var end: usize = 5;
    const slice = ptr[start..end];
    slice[2] = 3;
    try expect(slice[2] == 3);
    // The slice is mutable because we sliced a mutable pointer.
    try expect(@TypeOf(slice) == []u8);

    // Again, slicing with comptime-known indexes will produce another pointer
    // to an array:
    const ptr2 = slice[2..3];
    try expect(ptr2.len == 1);
    try expect(ptr2[0] == 3);
    try expect(@TypeOf(ptr2) == *[1]u8);
}

$ zig test test_slices.zig
1/2 test.using slices for strings... OK
2/2 test.slice pointer... OK
All 2 tests passed.

const std = @import("std");
const expect = std.testing.expect;

test "null terminated slice" {
    const slice: [:0]const u8 = "hello";

    try expect(slice.len == 5);
    try expect(slice[5] == 0);
}

$ zig test test_null_terminated_slice.zig
1/1 test.null terminated slice... OK
All 1 tests passed.

const std = @import("std");
const expect = std.testing.expect;

test "null terminated slicing" {
    var array = [_]u8{ 3, 2, 1, 0, 3, 2, 1, 0 };
    var runtime_length: usize = 3;
    const slice = array[0..runtime_length :0];

    try expect(@TypeOf(slice) == [:0]u8);
    try expect(slice.len == 3);
}

$ zig test test_null_terminated_slicing.zig
1/1 test.null terminated slicing... OK
All 1 tests passed.

const std = @import("std");
const expect = std.testing.expect;

test "sentinel mismatch" {
    var array = [_]u8{ 3, 2, 1, 0 };

    // Creating a sentinel-terminated slice from the array with a length of 2
    // will result in the value `1` occupying the sentinel element position.
    // This does not match the indicated sentinel value of `0` and will lead
    // to a runtime panic.
    var runtime_length: usize = 2;
    const slice = array[0..runtime_length :0];

    _ = slice;
}

$ zig test test_sentinel_mismatch.zig
1/1 test.sentinel mismatch... thread 873 panic: sentinel mismatch: expected 0, found 1
/builddir/build/BUILD/zig-0.11.0/docgen_tmp/test_sentinel_mismatch.zig:12:24: 0x224316 in test.sentinel mismatch (test)
    const slice = array[0..runtime_length :0];
                       ^
/builddir/build/BUILD/zig-0.11.0/redhat-linux-build/stage3/lib/zig/test_runner.zig:176:28: 0x22db05 in mainTerminal (test)
        } else test_fn.func();
                           ^
/builddir/build/BUILD/zig-0.11.0/redhat-linux-build/stage3/lib/zig/test_runner.zig:36:28: 0x225ada in main (test)
        return mainTerminal();
                           ^
/builddir/build/BUILD/zig-0.11.0/redhat-linux-build/stage3/lib/zig/std/start.zig:564:22: 0x224912 in posixCallMainAndExit (test)
            root.main();
                     ^
/builddir/build/BUILD/zig-0.11.0/redhat-linux-build/stage3/lib/zig/std/start.zig:243:5: 0x224461 in _start (test)
    asm volatile (switch (native_arch) {
    ^
???:?:?: 0x0 in ??? (???)
error: the following test command crashed:
/builddir/build/BUILD/zig-0.11.0/zig-cache/o/296f29142befd7c6cdbbaff0c53548ae/test

// Declare a struct.
// Zig gives no guarantees about the order of fields and the size of
// the struct but the fields are guaranteed to be ABI-aligned.
const Point = struct {
    x: f32,
    y: f32,
};

// Maybe we want to pass it to OpenGL so we want to be particular about
// how the bytes are arranged.
const Point2 = packed struct {
    x: f32,
    y: f32,
};


// Declare an instance of a struct.
const p = Point {
    .x = 0.12,
    .y = 0.34,
};

// Maybe we're not ready to fill out some of the fields.
var p2 = Point {
    .x = 0.12,
    .y = undefined,
};

// Structs can have methods
// Struct methods are not special, they are only namespaced
// functions that you can call with dot syntax.
const Vec3 = struct {
    x: f32,
    y: f32,
    z: f32,

    pub fn init(x: f32, y: f32, z: f32) Vec3 {
        return Vec3 {
            .x = x,
            .y = y,
            .z = z,
        };
    }

    pub fn dot(self: Vec3, other: Vec3) f32 {
        return self.x * other.x + self.y * other.y + self.z * other.z;
    }
};

const expect = @import("std").testing.expect;
test "dot product" {
    const v1 = Vec3.init(1.0, 0.0, 0.0);
    const v2 = Vec3.init(0.0, 1.0, 0.0);
    try expect(v1.dot(v2) == 0.0);

    // Other than being available to call with dot syntax, struct methods are
    // not special. You can reference them as any other declaration inside
    // the struct:
    try expect(Vec3.dot(v1, v2) == 0.0);
}

// Structs can have declarations.
// Structs can have 0 fields.
const Empty = struct {
    pub const PI = 3.14;
};
test "struct namespaced variable" {
    try expect(Empty.PI == 3.14);
    try expect(@sizeOf(Empty) == 0);

    // you can still instantiate an empty struct
    const does_nothing = Empty {};

    _ = does_nothing;
}

// struct field order is determined by the compiler for optimal performance.
// however, you can still calculate a struct base pointer given a field pointer:
fn setYBasedOnX(x: *f32, y: f32) void {
    const point = @fieldParentPtr(Point, "x", x);
    point.y = y;
}
test "field parent pointer" {
    var point = Point {
        .x = 0.1234,
        .y = 0.5678,
    };
    setYBasedOnX(&point.x, 0.9);
    try expect(point.y == 0.9);
}

// You can return a struct from a function. This is how we do generics
// in Zig:
fn LinkedList(comptime T: type) type {
    return struct {
        pub const Node = struct {
            prev: ?*Node,
            next: ?*Node,
            data: T,
        };

        first: ?*Node,
        last:  ?*Node,
        len:   usize,
    };
}

test "linked list" {
    // Functions called at compile-time are memoized. This means you can
    // do this:
    try expect(LinkedList(i32) == LinkedList(i32));

    var list = LinkedList(i32) {
        .first = null,
        .last = null,
        .len = 0,
    };
    try expect(list.len == 0);

    // Since types are first class values you can instantiate the type
    // by assigning it to a variable:
    const ListOfInts = LinkedList(i32);
    try expect(ListOfInts == LinkedList(i32));

    var node = ListOfInts.Node {
        .prev = null,
        .next = null,
        .data = 1234,
    };
    var list2 = LinkedList(i32) {
        .first = &node,
        .last = &node,
        .len = 1,
    };

    // When using a pointer to a struct, fields can be accessed directly,
    // without explicitly dereferencing the pointer.
    // So you can do
    try expect(list2.first.?.data == 1234);
    // instead of try expect(list2.first.?.*.data == 1234);
}

$ zig test test_structs.zig
1/4 test.dot product... OK
2/4 test.struct namespaced variable... OK
3/4 test.field parent pointer... OK
4/4 test.linked list... OK
All 4 tests passed.

const Foo = struct {
    a: i32 = 1234,
    b: i32,
};

test "default struct initialization fields" {
    const x = Foo{
        .b = 5,
    };
    if (x.a + x.b != 1239) {
        @compileError("it's even comptime-known!");
    }
}

$ zig test test_struct_default_field_values.zig
1/1 test.default struct initialization fields... OK
All 1 tests passed.

const std = @import("std");
const native_endian = @import("builtin").target.cpu.arch.endian();
const expect = std.testing.expect;

const Full = packed struct {
    number: u16,
};
const Divided = packed struct {
    half1: u8,
    quarter3: u4,
    quarter4: u4,
};

test "@bitCast between packed structs" {
    try doTheTest();
    try comptime doTheTest();
}

fn doTheTest() !void {
    try expect(@sizeOf(Full) == 2);
    try expect(@sizeOf(Divided) == 2);
    var full = Full{ .number = 0x1234 };
    var divided: Divided = @bitCast(full);
    try expect(divided.half1 == 0x34);
    try expect(divided.quarter3 == 0x2);
    try expect(divided.quarter4 == 0x1);

    var ordered: [2]u8 = @bitCast(full);
    switch (native_endian) {
        .Big => {
            try expect(ordered[0] == 0x12);
            try expect(ordered[1] == 0x34);
        },
        .Little => {
            try expect(ordered[0] == 0x34);
            try expect(ordered[1] == 0x12);
        },
    }
}

$ zig test test_packed_structs.zig
1/1 test.@bitCast between packed structs... OK
All 1 tests passed.

const std = @import("std");
const expect = std.testing.expect;

const BitField = packed struct {
    a: u3,
    b: u3,
    c: u2,
};

var foo = BitField{
    .a = 1,
    .b = 2,
    .c = 3,
};

test "pointer to non-byte-aligned field" {
    const ptr = &foo.b;
    try expect(ptr.* == 2);
}

$ zig test test_pointer_to_non-byte_aligned_field.zig
1/1 test.pointer to non-byte-aligned field... OK
All 1 tests passed.

const std = @import("std");
const expect = std.testing.expect;

const BitField = packed struct {
    a: u3,
    b: u3,
    c: u2,
};

var bit_field = BitField{
    .a = 1,
    .b = 2,
    .c = 3,
};

test "pointer to non-bit-aligned field" {
    try expect(bar(&bit_field.b) == 2);
}

fn bar(x: *const u3) u3 {
    return x.*;
}

$ zig test test_misaligned_pointer.zig
docgen_tmp/test_misaligned_pointer.zig:17:20: error: expected type '*const u3', found '*align(1:3:1) u3'
    try expect(bar(&bit_field.b) == 2);
                   ^~~~~~~~~~~~
docgen_tmp/test_misaligned_pointer.zig:17:20: note: pointer host size '1' cannot cast into pointer host size '0'
docgen_tmp/test_misaligned_pointer.zig:17:20: note: pointer bit offset '3' cannot cast into pointer bit offset '0'
docgen_tmp/test_misaligned_pointer.zig:20:11: note: parameter type declared here
fn bar(x: *const u3) u3 {
          ^~~~~~~~~

const std = @import("std");
const expect = std.testing.expect;

const BitField = packed struct {
    a: u3,
    b: u3,
    c: u2,
};

var bit_field = BitField{
    .a = 1,
    .b = 2,
    .c = 3,
};

test "pointers of sub-byte-aligned fields share addresses" {
    try expect(@intFromPtr(&bit_field.a) == @intFromPtr(&bit_field.b));
    try expect(@intFromPtr(&bit_field.a) == @intFromPtr(&bit_field.c));
}

$ zig test test_packed_struct_field_address.zig
1/1 test.pointers of sub-byte-aligned fields share addresses... OK
All 1 tests passed.

const std = @import("std");
const expect = std.testing.expect;

const BitField = packed struct {
    a: u3,
    b: u3,
    c: u2,
};

test "pointer to non-bit-aligned field" {
    comptime {
        try expect(@bitOffsetOf(BitField, "a") == 0);
        try expect(@bitOffsetOf(BitField, "b") == 3);
        try expect(@bitOffsetOf(BitField, "c") == 6);

        try expect(@offsetOf(BitField, "a") == 0);
        try expect(@offsetOf(BitField, "b") == 0);
        try expect(@offsetOf(BitField, "c") == 0);
    }
}

$ zig test test_bitOffsetOf_offsetOf.zig
1/1 test.pointer to non-bit-aligned field... OK
All 1 tests passed.

const std = @import("std");
const expect = std.testing.expect;

const S = packed struct {
    a: u32,
    b: u32,
};
test "overaligned pointer to packed struct" {
    var foo: S align(4) = .{ .a = 1, .b = 2 };
    const ptr: *align(4) S = &foo;
    const ptr_to_b: *u32 = &ptr.b;
    try expect(ptr_to_b.* == 2);
}

$ zig test test_overaligned_packed_struct.zig
1/1 test.overaligned pointer to packed struct... OK
All 1 tests passed.

const std = @import("std");
const expectEqual = std.testing.expectEqual;

test "aligned struct fields" {
    const S = struct {
        a: u32 align(2),
        b: u32 align(64),
    };
    var foo = S{ .a = 1, .b = 2 };

    try expectEqual(64, @alignOf(S));
    try expectEqual(*align(2) u32, @TypeOf(&foo.a));
    try expectEqual(*align(64) u32, @TypeOf(&foo.b));
}

$ zig test test_aligned_struct_fields.zig
1/1 test.aligned struct fields... OK
All 1 tests passed.

const std = @import("std");

pub fn main() void {
    const Foo = struct {};
    std.debug.print("variable: {s}\n", .{@typeName(Foo)});
    std.debug.print("anonymous: {s}\n", .{@typeName(struct {})});
    std.debug.print("function: {s}\n", .{@typeName(List(i32))});
}

fn List(comptime T: type) type {
    return struct {
        x: T,
    };
}

$ zig build-exe struct_name.zig
$ ./struct_name
variable: struct_name.main.Foo
anonymous: struct_name.main__struct_3482
function: struct_name.List(i32)

const std = @import("std");
const expect = std.testing.expect;

const Point = struct {x: i32, y: i32};

test "anonymous struct literal" {
    var pt: Point = .{
        .x = 13,
        .y = 67,
    };
    try expect(pt.x == 13);
    try expect(pt.y == 67);
}

$ zig test test_struct_result.zig
1/1 test.anonymous struct literal... OK
All 1 tests passed.

const std = @import("std");
const expect = std.testing.expect;

test "fully anonymous struct" {
    try dump(.{
        .int = @as(u32, 1234),
        .float = @as(f64, 12.34),
        .b = true,
        .s = "hi",
    });
}

fn dump(args: anytype) !void {
    try expect(args.int == 1234);
    try expect(args.float == 12.34);
    try expect(args.b);
    try expect(args.s[0] == 'h');
    try expect(args.s[1] == 'i');
}

$ zig test test_anonymous_struct.zig
1/1 test.fully anonymous struct... OK
All 1 tests passed.

const std = @import("std");
const expect = std.testing.expect;

test "tuple" {
    const values = .{
        @as(u32, 1234),
        @as(f64, 12.34),
        true,
        "hi",
    } ++ .{false} ** 2;
    try expect(values[0] == 1234);
    try expect(values[4] == false);
    inline for (values, 0..) |v, i| {
        if (i != 2) continue;
        try expect(v);
    }
    try expect(values.len == 6);
    try expect(values.@"3"[0] == 'h');
}

$ zig test test_tuples.zig
1/1 test.tuple... OK
All 1 tests passed.

const expect = @import("std").testing.expect;
const mem = @import("std").mem;

// Declare an enum.
const Type = enum {
    ok,
    not_ok,
};

// Declare a specific enum field.
const c = Type.ok;

// If you want access to the ordinal value of an enum, you
// can specify the tag type.
const Value = enum(u2) {
    zero,
    one,
    two,
};
// Now you can cast between u2 and Value.
// The ordinal value starts from 0, counting up by 1 from the previous member.
test "enum ordinal value" {
    try expect(@intFromEnum(Value.zero) == 0);
    try expect(@intFromEnum(Value.one) == 1);
    try expect(@intFromEnum(Value.two) == 2);
}

// You can override the ordinal value for an enum.
const Value2 = enum(u32) {
    hundred = 100,
    thousand = 1000,
    million = 1000000,
};
test "set enum ordinal value" {
    try expect(@intFromEnum(Value2.hundred) == 100);
    try expect(@intFromEnum(Value2.thousand) == 1000);
    try expect(@intFromEnum(Value2.million) == 1000000);
}

// You can also override only some values.
const Value3 = enum(u4) {
    a,
    b = 8,
    c,
    d = 4,
    e,
};
test "enum implicit ordinal values and overridden values" {
    try expect(@intFromEnum(Value3.a) == 0);
    try expect(@intFromEnum(Value3.b) == 8);
    try expect(@intFromEnum(Value3.c) == 9);
    try expect(@intFromEnum(Value3.d) == 4);
    try expect(@intFromEnum(Value3.e) == 5);
}

// Enums can have methods, the same as structs and unions.
// Enum methods are not special, they are only namespaced
// functions that you can call with dot syntax.
const Suit = enum {
    clubs,
    spades,
    diamonds,
    hearts,

    pub fn isClubs(self: Suit) bool {
        return self == Suit.clubs;
    }
};
test "enum method" {
    const p = Suit.spades;
    try expect(!p.isClubs());
}

// An enum can be switched upon.
const Foo = enum {
    string,
    number,
    none,
};
test "enum switch" {
    const p = Foo.number;
    const what_is_it = switch (p) {
        Foo.string => "this is a string",
        Foo.number => "this is a number",
        Foo.none => "this is a none",
    };
    try expect(mem.eql(u8, what_is_it, "this is a number"));
}

// @typeInfo can be used to access the integer tag type of an enum.
const Small = enum {
    one,
    two,
    three,
    four,
};
test "std.meta.Tag" {
    try expect(@typeInfo(Small).Enum.tag_type == u2);
}

// @typeInfo tells us the field count and the fields names:
test "@typeInfo" {
    try expect(@typeInfo(Small).Enum.fields.len == 4);
    try expect(mem.eql(u8, @typeInfo(Small).Enum.fields[1].name, "two"));
}

// @tagName gives a [:0]const u8 representation of an enum value:
test "@tagName" {
    try expect(mem.eql(u8, @tagName(Small.three), "three"));
}

$ zig test test_enums.zig
1/8 test.enum ordinal value... OK
2/8 test.set enum ordinal value... OK
3/8 test.enum implicit ordinal values and overridden values... OK
4/8 test.enum method... OK
5/8 test.enum switch... OK
6/8 test.std.meta.Tag... OK
7/8 test.@typeInfo... OK
8/8 test.@tagName... OK
All 8 tests passed.

const Foo = enum { a, b, c };
export fn entry(foo: Foo) void { _ = foo; }

$ zig build-obj enum_export_error.zig
docgen_tmp/enum_export_error.zig:2:17: error: parameter of type 'enum_export_error.Foo' not allowed in function with calling convention 'C'
export fn entry(foo: Foo) void { _ = foo; }
                ^~~~~~~~
docgen_tmp/enum_export_error.zig:2:17: note: enum tag type 'u2' is not extern compatible
docgen_tmp/enum_export_error.zig:2:17: note: only integers with 0, 8, 16, 32, 64 and 128 bits are extern compatible
docgen_tmp/enum_export_error.zig:1:13: note: enum declared here
const Foo = enum { a, b, c };
            ^~~~~~~~~~~~~~~~

const Foo = enum(c_int) { a, b, c };
export fn entry(foo: Foo) void { _ = foo; }

$ zig build-obj enum_export.zig

const std = @import("std");
const expect = std.testing.expect;

const Color = enum {
    auto,
    off,
    on,
};

test "enum literals" {
    const color1: Color = .auto;
    const color2 = Color.auto;
    try expect(color1 == color2);
}

test "switch using enum literals" {
    const color = Color.on;
    const result = switch (color) {
        .auto => false,
        .on => true,
        .off => false,
    };
    try expect(result);
}

$ zig test test_enum_literals.zig
1/2 test.enum literals... OK
2/2 test.switch using enum literals... OK
All 2 tests passed.

const std = @import("std");
const expect = std.testing.expect;

const Number = enum(u8) {
    one,
    two,
    three,
    _,
};

test "switch on non-exhaustive enum" {
    const number = Number.one;
    const result = switch (number) {
        .one => true,
        .two,
        .three => false,
        _ => false,
    };
    try expect(result);
    const is_one = switch (number) {
        .one => true,
        else => false,
    };
    try expect(is_one);
}

$ zig test test_switch_non-exhaustive.zig
1/1 test.switch on non-exhaustive enum... OK
All 1 tests passed.

const Payload = union {
    int: i64,
    float: f64,
    boolean: bool,
};
test "simple union" {
    var payload = Payload{ .int = 1234 };
    payload.float = 12.34;
}

$ zig test test_wrong_union_access.zig
1/1 test.simple union... thread 1069 panic: access of union field 'float' while field 'int' is active
/builddir/build/BUILD/zig-0.11.0/docgen_tmp/test_wrong_union_access.zig:8:12: 0x224337 in test.simple union (test)
    payload.float = 12.34;
           ^
/builddir/build/BUILD/zig-0.11.0/redhat-linux-build/stage3/lib/zig/test_runner.zig:176:28: 0x22d4f5 in mainTerminal (test)
        } else test_fn.func();
                           ^
/builddir/build/BUILD/zig-0.11.0/redhat-linux-build/stage3/lib/zig/test_runner.zig:36:28: 0x22555a in main (test)
        return mainTerminal();
                           ^
/builddir/build/BUILD/zig-0.11.0/redhat-linux-build/stage3/lib/zig/std/start.zig:564:22: 0x2248f2 in posixCallMainAndExit (test)
            root.main();
                     ^
/builddir/build/BUILD/zig-0.11.0/redhat-linux-build/stage3/lib/zig/std/start.zig:243:5: 0x224441 in _start (test)
    asm volatile (switch (native_arch) {
    ^
???:?:?: 0x0 in ??? (???)
error: the following test command crashed:
/builddir/build/BUILD/zig-0.11.0/zig-cache/o/8b74ae40a8cc827827d07d3798381471/test

const std = @import("std");
const expect = std.testing.expect;

const Payload = union {
    int: i64,
    float: f64,
    boolean: bool,
};
test "simple union" {
    var payload = Payload{ .int = 1234 };
    try expect(payload.int == 1234);
    payload = Payload{ .float = 12.34 };
    try expect(payload.float == 12.34);
}

$ zig test test_simple_union.zig
1/1 test.simple union... OK
All 1 tests passed.

const std = @import("std");
const expect = std.testing.expect;

const ComplexTypeTag = enum {
    ok,
    not_ok,
};
const ComplexType = union(ComplexTypeTag) {
    ok: u8,
    not_ok: void,
};

test "switch on tagged union" {
    const c = ComplexType{ .ok = 42 };
    try expect(@as(ComplexTypeTag, c) == ComplexTypeTag.ok);

    switch (c) {
        ComplexTypeTag.ok => |value| try expect(value == 42),
        ComplexTypeTag.not_ok => unreachable,
    }
}

test "get tag type" {
    try expect(std.meta.Tag(ComplexType) == ComplexTypeTag);
}

$ zig test test_tagged_union.zig
1/2 test.switch on tagged union... OK
2/2 test.get tag type... OK
All 2 tests passed.

const std = @import("std");
const expect = std.testing.expect;

const ComplexTypeTag = enum {
    ok,
    not_ok,
};
const ComplexType = union(ComplexTypeTag) {
    ok: u8,
    not_ok: void,
};

test "modify tagged union in switch" {
    var c = ComplexType{ .ok = 42 };

    switch (c) {
        ComplexTypeTag.ok => |*value| value.* += 1,
        ComplexTypeTag.not_ok => unreachable,
    }

    try expect(c.ok == 43);
}

$ zig test test_switch_modify_tagged_union.zig
1/1 test.modify tagged union in switch... OK
All 1 tests passed.

const std = @import("std");
const expect = std.testing.expect;

const Variant = union(enum) {
    int: i32,
    boolean: bool,

    // void can be omitted when inferring enum tag type.
    none,

    fn truthy(self: Variant) bool {
        return switch (self) {
            Variant.int => |x_int| x_int != 0,
            Variant.boolean => |x_bool| x_bool,
            Variant.none => false,
        };
    }
};

test "union method" {
    var v1 = Variant{ .int = 1 };
    var v2 = Variant{ .boolean = false };

    try expect(v1.truthy());
    try expect(!v2.truthy());
}

$ zig test test_union_method.zig
1/1 test.union method... OK
All 1 tests passed.

const std = @import("std");
const expect = std.testing.expect;

const Small2 = union(enum) {
    a: i32,
    b: bool,
    c: u8,
};
test "@tagName" {
    try expect(std.mem.eql(u8, @tagName(Small2.a), "a"));
}

$ zig test test_tagName.zig
1/1 test.@tagName... OK
All 1 tests passed.

const std = @import("std");
const expect = std.testing.expect;

const Number = union {
    int: i32,
    float: f64,
};

test "anonymous union literal syntax" {
    var i: Number = .{.int = 42};
    var f = makeNumber();
    try expect(i.int == 42);
    try expect(f.float == 12.34);
}

fn makeNumber() Number {
    return .{.float = 12.34};
}

$ zig test test_anonymous_union.zig
1/1 test.anonymous union literal syntax... OK
All 1 tests passed.

const Derp = opaque {};
const Wat = opaque {};

extern fn bar(d: *Derp) void;
fn foo(w: *Wat) callconv(.C) void {
    bar(w);
}

test "call foo" {
    foo(undefined);
}

$ zig test test_opaque.zig
docgen_tmp/test_opaque.zig:6:9: error: expected type '*test_opaque.Derp', found '*test_opaque.Wat'
    bar(w);
        ^
docgen_tmp/test_opaque.zig:6:9: note: pointer type child 'test_opaque.Wat' cannot cast into pointer type child 'test_opaque.Derp'
docgen_tmp/test_opaque.zig:2:13: note: opaque declared here
const Wat = opaque {};
            ^~~~~~~~~
docgen_tmp/test_opaque.zig:1:14: note: opaque declared here
const Derp = opaque {};
             ^~~~~~~~~
docgen_tmp/test_opaque.zig:4:18: note: parameter type declared here
extern fn bar(d: *Derp) void;
                 ^~~~~
referenced by:
    test.call foo: docgen_tmp/test_opaque.zig:10:5
    remaining reference traces hidden; use '-freference-trace' to see all reference traces

test "access variable after block scope" {
    {
        var x: i32 = 1;
        _ = x;
    }
    x += 1;
}

$ zig test test_blocks.zig
docgen_tmp/test_blocks.zig:6:5: error: use of undeclared identifier 'x'
    x += 1;
    ^

const std = @import("std");
const expect = std.testing.expect;

test "labeled break from labeled block expression" {
    var y: i32 = 123;

    const x = blk: {
        y += 1;
        break :blk y;
    };
    try expect(x == 124);
    try expect(y == 124);
}

$ zig test test_labeled_break.zig
1/1 test.labeled break from labeled block expression... OK
All 1 tests passed.

const pi = 3.14;

test "inside test block" {
    // Let's even go inside another block
    {
        var pi: i32 = 1234;
    }
}

$ zig test test_shadowing.zig
docgen_tmp/test_shadowing.zig:6:13: error: local variable shadows declaration of 'pi'
        var pi: i32 = 1234;
            ^~
docgen_tmp/test_shadowing.zig:1:1: note: declared here
const pi = 3.14;
^~~~~~~~~~~~~~~

test "separate scopes" {
    {
        const pi = 3.14;
        _ = pi;
    }
    {
        var pi: bool = true;
        _ = pi;
    }
}

$ zig test test_scopes.zig
1/1 test.separate scopes... OK
All 1 tests passed.

const std = @import("std");
const expect = std.testing.expect;

test {
    const a = {};
    const b = void{};
    try expect(@TypeOf(a) == void);
    try expect(@TypeOf(b) == void);
    try expect(a == b);
}

$ zig test test_empty_block.zig
1/1 test_0... OK
All 1 tests passed.

const std = @import("std");
const builtin = @import("builtin");
const expect = std.testing.expect;

test "switch simple" {
    const a: u64 = 10;
    const zz: u64 = 103;

    // All branches of a switch expression must be able to be coerced to a
    // common type.
    //
    // Branches cannot fallthrough. If fallthrough behavior is desired, combine
    // the cases and use an if.
    const b = switch (a) {
        // Multiple cases can be combined via a ','
        1, 2, 3 => 0,

        // Ranges can be specified using the ... syntax. These are inclusive
        // of both ends.
        5...100 => 1,

        // Branches can be arbitrarily complex.
        101 => blk: {
            const c: u64 = 5;
            break :blk c * 2 + 1;
        },

        // Switching on arbitrary expressions is allowed as long as the
        // expression is known at compile-time.
        zz => zz,
        blk: {
            const d: u32 = 5;
            const e: u32 = 100;
            break :blk d + e;
        } => 107,

        // The else branch catches everything not already captured.
        // Else branches are mandatory unless the entire range of values
        // is handled.
        else => 9,
    };

    try expect(b == 1);
}

// Switch expressions can be used outside a function:
const os_msg = switch (builtin.target.os.tag) {
    .linux => "we found a linux user",
    else => "not a linux user",
};

// Inside a function, switch statements implicitly are compile-time
// evaluated if the target expression is compile-time known.
test "switch inside function" {
    switch (builtin.target.os.tag) {
        .fuchsia => {
            // On an OS other than fuchsia, block is not even analyzed,
            // so this compile error is not triggered.
            // On fuchsia this compile error would be triggered.
            @compileError("fuchsia not supported");
        },
        else => {},
    }
}

$ zig test test_switch.zig
1/2 test.switch simple... OK
2/2 test.switch inside function... OK
All 2 tests passed.

const expect = @import("std").testing.expect;

test "switch on tagged union" {
    const Point = struct {
        x: u8,
        y: u8,
    };
    const Item = union(enum) {
        a: u32,
        c: Point,
        d,
        e: u32,
    };

    var a = Item{ .c = Point{ .x = 1, .y = 2 } };

    // Switching on more complex enums is allowed.
    const b = switch (a) {
        // A capture group is allowed on a match, and will return the enum
        // value matched. If the payload types of both cases are the same
        // they can be put into the same switch prong.
        Item.a, Item.e => |item| item,

        // A reference to the matched value can be obtained using `*` syntax.
        Item.c => |*item| blk: {
            item.*.x += 1;
            break :blk 6;
        },

        // No else is required if the types cases was exhaustively handled
        Item.d => 8,
    };

    try expect(b == 6);
    try expect(a.c.x == 2);
}

$ zig test test_switch_tagged_union.zig
1/1 test.switch on tagged union... OK
All 1 tests passed.

const Color = enum {
    auto,
    off,
    on,
};

test "exhaustive switching" {
    const color = Color.off;
    switch (color) {
        Color.auto => {},
        Color.on => {},
    }
}

$ zig test test_unhandled_enumeration_value.zig
docgen_tmp/test_unhandled_enumeration_value.zig:9:5: error: switch must handle all possibilities
    switch (color) {
    ^~~~~~
docgen_tmp/test_unhandled_enumeration_value.zig:3:5: note: unhandled enumeration value: 'off'
    off,
    ^~~
docgen_tmp/test_unhandled_enumeration_value.zig:1:15: note: enum 'test_unhandled_enumeration_value.Color' declared here
const Color = enum {
              ^~~~

const std = @import("std");
const expect = std.testing.expect;

const Color = enum {
    auto,
    off,
    on,
};

test "enum literals with switch" {
    const color = Color.off;
    const result = switch (color) {
        .auto => false,
        .on => false,
        .off => true,
    };
    try expect(result);
}

$ zig test test_exhaustive_switch.zig
1/1 test.enum literals with switch... OK
All 1 tests passed.

const std = @import("std");
const expect = std.testing.expect;
const expectError = std.testing.expectError;

fn isFieldOptional(comptime T: type, field_index: usize) !bool {
    const fields = @typeInfo(T).Struct.fields;
    return switch (field_index) {
        // This prong is analyzed `fields.len - 1` times with `idx` being a
        // unique comptime-known value each time.
        inline 0...fields.len - 1 => |idx| @typeInfo(fields[idx].type) == .Optional,
        else => return error.IndexOutOfBounds,
    };
}

const Struct1 = struct { a: u32, b: ?u32 };

test "using @typeInfo with runtime values" {
    var index: usize = 0;
    try expect(!try isFieldOptional(Struct1, index));
    index += 1;
    try expect(try isFieldOptional(Struct1, index));
    index += 1;
    try expectError(error.IndexOutOfBounds, isFieldOptional(Struct1, index));
}

// Calls to `isFieldOptional` on `Struct1` get unrolled to an equivalent
// of this function:
fn isFieldOptionalUnrolled(field_index: usize) !bool {
    return switch (field_index) {
        0 => false,
        1 => true,
        else => return error.IndexOutOfBounds,
    };
}

$ zig test test_inline_switch.zig
1/1 test.using @typeInfo with runtime values... OK
All 1 tests passed.

const std = @import("std");
const expect = std.testing.expect;

const SliceTypeA = extern struct {
    len: usize,
    ptr: [*]u32,
};
const SliceTypeB = extern struct {
    ptr: [*]SliceTypeA,
    len: usize,
};
const AnySlice = union(enum) {
    a: SliceTypeA,
    b: SliceTypeB,
    c: []const u8,
    d: []AnySlice,
};

fn withFor(any: AnySlice) usize {
    const Tag = @typeInfo(AnySlice).Union.tag_type.?;
    inline for (@typeInfo(Tag).Enum.fields) |field| {
        // With `inline for` the function gets generated as
        // a series of `if` statements relying on the optimizer
        // to convert it to a switch.
        if (field.value == @intFromEnum(any)) {
            return @field(any, field.name).len;
        }
    }
    // When using `inline for` the compiler doesn't know that every
    // possible case has been handled requiring an explicit `unreachable`.
    unreachable;
}

fn withSwitch(any: AnySlice) usize {
    return switch (any) {
        // With `inline else` the function is explicitly generated
        // as the desired switch and the compiler can check that
        // every possible case is handled.
        inline else => |slice| slice.len,
    };
}

test "inline for and inline else similarity" {
    var any = AnySlice{ .c = "hello" };
    try expect(withFor(any) == 5);
    try expect(withSwitch(any) == 5);
}

$ zig test test_inline_else.zig
1/1 test.inline for and inline else similarity... OK
All 1 tests passed.

const std = @import("std");
const expect = std.testing.expect;

const U = union(enum) {
    a: u32,
    b: f32,
};

fn getNum(u: U) u32 {
    switch (u) {
        // Here `num` is a runtime-known value that is either
        // `u.a` or `u.b` and `tag` is `u`'s comptime-known tag value.
        inline else => |num, tag| {
            if (tag == .b) {
                return @intFromFloat(num);
            }
            return num;
        }
    }
}

test "test" {
    var u = U{ .b = 42 };
    try expect(getNum(u) == 42);
}

$ zig test test_inline_switch_union_tag.zig
1/1 test.test... OK
All 1 tests passed.

const expect = @import("std").testing.expect;

test "while basic" {
    var i: usize = 0;
    while (i < 10) {
        i += 1;
    }
    try expect(i == 10);
}

$ zig test test_while.zig
1/1 test.while basic... OK
All 1 tests passed.