search

BruceChen7 / gitblog

My blog
6 stars 1 forks source link

zig基本知识 #40

Open BruceChen7 opened 1 year ago

BruceChen7 commented 1 year ago

资料

字符串

if

// If expressions have three uses, corresponding to the three types:
// * bool
// * ?T
// * anyerror!T

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

test "if expression" {
    // If expressions are used instead of a ternary expression.
    const a: u32 = 5;
    const b: u32 = 4;
    const result = if (a != b) 47 else 3089;
    try expect(result == 47);
}

test "if boolean" {
    // If expressions test boolean conditions.
    const a: u32 = 5;
    const b: u32 = 4;
    if (a != b) {
        try expect(true);
    } else if (a == 9) {
        unreachable;
    } else {
        unreachable;
    }
}

test "if optional" {
    // If expressions test for null.

    const a: ?u32 = 0;
    if (a) |value| {
        try expect(value == 0);
    } else {
        unreachable;
    }

    const b: ?u32 = null;
    if (b) |value| {
        unreachable;
    } else {
        try expect(true);
    }

    // The else is not required.
    if (a) |value| {
        try expect(value == 0);
    }

    // To test against null only, use the binary equality operator.
    if (b == null) {
        try expect(true);
    }

    // Access the value by reference using a pointer capture.
    var c: ?u32 = 3;
    if (c) |*value| {
        value.* = 2;
    }

    if (c) |value| {
        try expect(value == 2);
    } else {
        unreachable;
    }
}

test "if error union" {
    // If expressions test for errors.
    // Note the |err| capture on the else.

    const a: anyerror!u32 = 0;
    if (a) |value| {
        try expect(value == 0);
    } else |err| {
        unreachable;
    }

    const b: anyerror!u32 = error.BadValue;
    if (b) |value| {
        unreachable;
    } else |err| {
        try expect(err == error.BadValue);
    }

    // The else and |err| capture is strictly required.
    if (a) |value| {
        try expect(value == 0);
    } else |_| {}

    // To check only the error value, use an empty block expression.
    if (b) |_| {} else |err| {
        try expect(err == error.BadValue);
    }

    // Access the value by reference using a pointer capture.
    var c: anyerror!u32 = 3;
    if (c) |*value| {
        value.* = 9;
    } else |err| {
        unreachable;
    }

    if (c) |value| {
        try expect(value == 9);
    } else |err| {
        unreachable;
    }
}

test "if error union with optional" {
    // If expressions test for errors before unwrapping optionals.
    // The |optional_value| capture's type is ?u32.

    const a: anyerror!?u32 = 0;
    if (a) |optional_value| {
        try expect(optional_value.? == 0);
    } else |err| {
        unreachable;
    }

    const b: anyerror!?u32 = null;
    if (b) |optional_value| {
        try expect(optional_value == null);
    } else |err| {
        unreachable;
    }

    const c: anyerror!?u32 = error.BadValue;
    if (c) |optional_value| {
        unreachable;
    } else |err| {
        try expect(err == error.BadValue);
    }

    // Access the value by reference by using a pointer capture each time.
    var d: anyerror!?u32 = 3;
    if (d) |*optional_value| {
        if (optional_value.*) |*value| {
            value.* = 9;
        }
    } else |err| {
        unreachable;
    }

    if (d) |optional_value| {
        try expect(optional_value.? == 9);
    } else |err| {
        unreachable;
    }
}

for

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

test "for basics" {
    const items = [_]i32 { 4, 5, 3, 4, 0 };
    var sum: i32 = 0;

    // For loops iterate over slices and arrays.
    for (items) |value| {
        // Break and continue are supported.
        if (value == 0) {
            continue;
        }
        sum += value;
    }
    try expect(sum == 16);

    // To iterate over a portion of a slice, reslice.
    for (items[0..1]) |value| {
        sum += value;
    }
    try expect(sum == 20);

    // To access the index of iteration, specify a second capture value.
    // This is zero-indexed.
    var sum2: i32 = 0;
    for (items) |value, i| {
        try expect(@TypeOf(i) == usize);
        sum2 += @intCast(i32, i);
    }
    try expect(sum2 == 10);
}

test "for reference" {
    var items = [_]i32 { 3, 4, 2 };

    // Iterate over the slice by reference by
    // specifying that the capture value is a pointer.
    for (items) |*value| {
        value.* += 1;
    }

    try expect(items[0] == 4);
    try expect(items[1] == 5);
    try expect(items[2] == 3);
}

test "for else" {
    // For allows an else attached to it, the same as a while loop.
    var items = [_]?i32 { 3, 4, null, 5 };

    // For loops can also be used as expressions.
    // Similar to while loops, when you break from a for loop, the else branch is not evaluated.
    var sum: i32 = 0;
    const result = for (items) |value| {
        if (value != null) {
            sum += value.?;
        }
    } else blk: {
        try expect(sum == 12);
        break :blk sum;
    };
    try expect(result == 12);
}

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

test "nested break" {
    var count: usize = 0;
    outer: for ([_]i32{ 1, 2, 3, 4, 5 }) |_| {
        for ([_]i32{ 1, 2, 3, 4, 5 }) |_| {
            count += 1;
            break :outer;
        }
    }
    try expect(count == 1);
}

test "nested continue" {
    var count: usize = 0;
    outer: for ([_]i32{ 1, 2, 3, 4, 5, 6, 7, 8 }) |_| {
        for ([_]i32{ 1, 2, 3, 4, 5 }) |_| {
            count += 1;
            continue :outer;
        }
    }

    try expect(count == 8);
}

指针

Function Parameter Type Inference

comptime

pub fn Parser(comptime Value: type, comptime Reader: type) type {
    return struct {
        const Self = @This();
        _parse: fn(self: *Self, allocator: *Allocator, src: *Reader) callconv(.Inline) Error!?Value,

        pub fn parse(self: *Self, allocator: *Allocator, src: *Reader) callconv(.Inline) Error!?Value {
            return self._parse(self, allocator, src);
        }
    };
}

const parser: Parser([]u8, @TypeOf(reader)) = .{
    ._parse = myParse,
};

slice

enum

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

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

// Declare a specific instance of the enum variant.
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 for each member.
test "enum ordinal value" {
    try expect(@enumToInt(Value.zero) == 0);
    try expect(@enumToInt(Value.one) == 1);
    try expect(@enumToInt(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(@enumToInt(Value2.hundred) == 100);
    try expect(@enumToInt(Value2.thousand) == 1000);
    try expect(@enumToInt(Value2.million) == 1000000);
}

// 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 variant of different types can be switched upon.
const Foo = enum {
    string,
    number,
    none,
};
test "enum variant 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 []const u8 representation of an enum value:
test "@tagName" {
    try expect(mem.eql(u8, @tagName(Small.three), "three"));
}

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);
}

extern enum

non-exhaustive enum

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);
}

struct


// 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 global 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 {};
}

// 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,
    };
    try expect(list2.first.?.data == 1234);
}

union

error set type

Error Union Type

catch

fn doAThing(str: []u8) void {
    const number = parseU64(str, 10) catch 13;
    // ...
}

try

errdefer

在编译期间获取 error union 类型

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

test "error union" {
    var foo: anyerror!i32 = undefined;
    // Coerce from child type of an error union:
    foo = 1234;

    // Coerce from an error set:
    foo = error.SomeError;

    // Use compile-time reflection to access the payload type of an error union:
    comptime try expect(@typeInfo(@TypeOf(foo)).ErrorUnion.payload == i32);

    // Use compile-time reflection to access the error set type of an error union:
    comptime try expect(@typeInfo(@TypeOf(foo)).ErrorUnion.error_set == anyerror);
}

Error Return Traces

合并错误类型

const A = error{
    NotDir,

    /// A doc comment
    PathNotFound,
};
const B = error{
    OutOfMemory,

    /// B doc comment
    PathNotFound,
};

const C = A || B;

fn foo() C!void {
    return error.NotDir;
}

test "merge error sets" {
    if (foo()) {
        @panic("unexpected");
    } else |err| switch (err) {
        error.OutOfMemory => @panic("unexpected"),
        error.PathNotFound => @panic("unexpected"),
        error.NotDir => {},
    }
}

推断错误类型

// With an inferred error set
pub fn add_inferred(comptime T: type, a: T, b: T) !T {
    var answer: T = undefined;
    return if (@addWithOverflow(T, a, b, &answer)) error.Overflow else answer;
}

// With an explicit error set
pub fn add_explicit(comptime T: type, a: T, b: T) Error!T {
    var answer: T = undefined;
    return if (@addWithOverflow(T, a, b, &answer)) error.Overflow else answer;
}

const Error = error {
    Overflow,
};

const std = @import("std");

test "inferred error set" {
    if (add_inferred(u8, 255, 1)) |_| unreachable else |err| switch (err) {
        error.Overflow => {}, // ok
    }
}

optional

optional pointers

分配内存器的规则

build.zig

comptime

编译时期的代码消除

泛型

通用的 struct

@hasDecl

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);
    }
};

定义函数指针

pub fn binary_search_values_upsert_index(
    comptime Key: type,
    comptime Value: type,
    comptime key_from_value: fn (*const Value) callconv(.Inline) Key,
    values: []const Value,
    key: Key,
    comptime config: Config,
) u32

type/ziglang #public