Structs and Enums

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

// 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,
};

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

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;
    }
};

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);

    // Empty structs can be instantiated the same as usual.
    const does_nothing: Empty = .{};
    _ = does_nothing;
}

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

test "default struct initialization fields" {
    const x: Foo = .{
        .b = 5,
    };
    if (x.a + x.b != 1239) {
        comptime unreachable;
    }
}

fn setYBasedOnX(x: *f32, y: f32) void {
    const point: *Point = @fieldParentPtr("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);
}

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.
    try expect(LinkedList(i32) == LinkedList(i32));

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

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;

const Value = enum(u2) {
    zero,
    one,
    two,
};

test "enum ordinal value" {
    try expect(@intFromEnum(Value.zero) == 0);
    try expect(@intFromEnum(Value.one) == 1);
    try expect(@intFromEnum(Value.two) == 2);
}

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);
}

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());
}

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"));
}

const Small = enum {
    one,
    two,
    three,
    four,
};

test "std.meta.Tag" {
    try expect(@typeInfo(Small).@"enum".tag_type == u2);
}

test "@typeInfo" {
    try expect(@typeInfo(Small).@"enum".fields.len == 4);
    try expect(mem.eql(u8, @typeInfo(Small).@"enum".fields[1].name, "two"));
}

test "@tagName" {
    try expect(mem.eql(u8, @tagName(Small.three), "three"));
}