Zig has `comptime` where you effectively generate Zig code at compile time by writing Zig code, no special generics syntax/semantics needed. It is very nice and powerful concept that covers lots of ground that in Rust would belong to the land of procedural macros.

Functions in Zig can be called both in runtime and in compile-time. You can force some expression to be called during comptime using a keyword, and sometimes the comptime is implied (like when you define top-level const)

If a function is called in comptime, it can also return types. So for example:

    // this is a function which accepts a type
    // if you accept type, you also have to restrict the arg to be comptime
    // if the arg is comptime it still does not mean that the function cannot be called in runtime,
    // but in this case, it returns type, so it is comptime-only function
    // there are also cases where this is not true, like std.mem.eql(u8, a, b) which accepts type,
    // but can be called in runtime because it does not return type
    fn Wrapper(comptime T: type) type {
        return struct { value: T };
    }

    const F32Wrapper = Wrapper(f32);

    // @TypeOf(x.value) == f32
    var x: F32Wrapper = .{ value: 1.0 }