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coxmi • yesterday at 9:40 AM • 1 reply • view on HN

Yeah, after looking it up, it looks like it is basically only used as either field access or an 'infer operator', is that right?

I thought it was used in four completely separate ways:

· normal struct field access

· anonymous struct definition

· field definition within structs (for reasons to do with the parser)

· an extra 'infer operator' for syntactic sugar

But there's no support for anonymous structs/fields, and all structs and fields require a type somewhere for it to be inferred. Which is why this is invalid zig:

  const test = .{ .x = 0, .y = 1 };
(It would need the type to be specified in the called function definition, or inline when assigning)

Correct me if I'm wrong here! (And thank you)

Replies

tremon • yesterday at 2:49 PM

I don't think that "infer operator" is a special case of field access, to me it feels like regular known-type elision similar to how C# and C++ use the var keyword if the data type can be inferred from the rhs expression:

    const Enum = enum {one, two, five};
    const t: Enum = .one;  // Enum.one, but the type was inferred from lhs
    std.debug.print("{t}\n", .{t});
Defining an anonymous struct is valid in zig; your example is only invalid because "test" is a reserved keyword. But you are correct that it reifies into a concrete type, and after initialization it doesn't coerce into other types because zig doesn't do structural typing:

    const anonymous = .{ .x = 0, .y = 1 };
    std.debug.print("{}\n", .{@TypeOf(anonymous)}); // will output something like test_0__struct_45138

    const Point = struct { x: i32, y: i32 };
    const p1 = Point{ .x = 0, .y = 1 };  // valid, explicit struct literal
    const p2: Point = .{ .x = 0, .y = 1 };  // valid, anonymous struct will coerce to Point
    //const pt: Point = anonymous; // error: expected type 'test_0.Point', found 'test_0__struct_45138'
And then there's fieldless anonymous structs aka tuples. I'm including them because they were used in the print statements above:

    const tuple = .{ 0, "1", true };
    std.debug.print("{}\n", .{@TypeOf(tuple)});
    // struct { comptime comptime_int = 0, comptime *const [1:0]u8 = "1", comptime bool = true }
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