# Slices

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

test "basic slices" {
    var array = [_]i32{ 1, 2, 3, 4 };
    var known_at_runtime_zero: usize = 0;
    _ = &known_at_runtime_zero;
    const slice = array[known_at_runtime_zero..array.len];

    // alternative initialization using result location
    const alt_slice: []const i32 = &.{ 1, 2, 3, 4 };

    try expectEqualSlices(i32, slice, alt_slice);

    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;
    _ = &runtime_start;
    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.
    try expect(@TypeOf(&slice[0]) == *i32);
    // Using the `ptr` field gives a many-item pointer.
    try expect(@TypeOf(slice.ptr) == [*]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.

    // Empty slices can be created like this:
    const empty1 = &[0]u8{};
    // If the type is known you can use this short hand:
    const empty2: []u8 = &.{};
    try expect(empty1.len == 0);
    try expect(empty2.len == 0);

    // A zero-length initialization can always be used to create an empty slice, even if the slice is mutable.
    // This is because the pointed-to data is zero bits long, so its immutability is irrelevant.
}

$ zig test test_basic_slices.zig
1/1 test_basic_slices.test.basic slices...thread 2902466 panic: index out of bounds: index 10, len 4
/home/andy/dev/zig/doc/langref/test_basic_slices.zig:41:10: 0x102e3c0 in test.basic slices (test_basic_slices.zig)
    slice[10] += 1;
         ^
/home/andy/dev/zig/lib/compiler/test_runner.zig:218:25: 0x1160b60 in mainTerminal (test_runner.zig)
        if (test_fn.func()) |_| {
                        ^
/home/andy/dev/zig/lib/compiler/test_runner.zig:66:28: 0x1159d81 in main (test_runner.zig)
        return mainTerminal();
                           ^
/home/andy/dev/zig/lib/std/start.zig:618:22: 0x1153b1d in posixCallMainAndExit (std.zig)
            root.main();
                     ^
/home/andy/dev/zig/lib/std/start.zig:232:5: 0x11533b1 in _start (std.zig)
    asm volatile (switch (native_arch) {
    ^
???:?:?: 0x0 in ??? (???)
error: the following test command crashed:
/home/andy/dev/zig/.zig-cache/o/0e584e3dac6333a0b2d5158992704660/test --seed=0x665d12a2

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;
    _ = &start;
    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 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;
    _ = .{ &start, &end };
    const slice = ptr[start..end];
    // The slice is mutable because we sliced a mutable pointer.
    try expect(@TypeOf(slice) == []u8);
    slice[2] = 3;
    try expect(array[2] == 3);

    // 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_slices.test.using slices for strings...OK
2/2 test_slices.test.slice pointer...OK
All 2 tests passed.

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

test "0-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.test.0-terminated slice...OK
All 1 tests passed.

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

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

    _ = slice;
}

$ zig test test_sentinel_mismatch.zig
1/1 test_sentinel_mismatch.test.sentinel mismatch...thread 2902472 panic: sentinel mismatch: expected 0, found 1
/home/andy/dev/zig/doc/langref/test_sentinel_mismatch.zig:13:24: 0x102c117 in test.sentinel mismatch (test_sentinel_mismatch.zig)
    const slice = array[0..runtime_length :0];
                       ^
/home/andy/dev/zig/lib/compiler/test_runner.zig:218:25: 0x115cc90 in mainTerminal (test_runner.zig)
        if (test_fn.func()) |_| {
                        ^
/home/andy/dev/zig/lib/compiler/test_runner.zig:66:28: 0x1155eb1 in main (test_runner.zig)
        return mainTerminal();
                           ^
/home/andy/dev/zig/lib/std/start.zig:618:22: 0x114fc4d in posixCallMainAndExit (std.zig)
            root.main();
                     ^
/home/andy/dev/zig/lib/std/start.zig:232:5: 0x114f4e1 in _start (std.zig)
    asm volatile (switch (native_arch) {
    ^
???:?:?: 0x0 in ??? (???)
error: the following test command crashed:
/home/andy/dev/zig/.zig-cache/o/12c6cfa0971ea7c724c8448a09f20f6b/test --seed=0xb506c876