Why is @constCast a one-directional function?

Help
1

Why isn’t it bi-directional?

const print = @import("std").debug.print;

pub fn main() void {
    var v: usize = 123;
    const x = &v;
    print("{}\n", .{ @TypeOf(x) });// *usize
    const y = @constCast(x);
    print("{}\n", .{ @TypeOf(y) });// *usize
    
    const z: *const usize = y;
    print("{}\n", .{ @TypeOf(z) });// *const usize
    const w = @constCast(z);
    print("{}\n", .{ @TypeOf(w) });// *usize
}
2

Because pointers-to-var coerce to pointers-to-const without any checks or manipulation. It’s always safe and always a no-op. There’s no need for a builtin.

4 Likes
3

what do you mean bi-directional? if you mean var -> const then the builtin should be named @constToggle()

4

because

var v: usize = 123;
const x = &v; // *usize
// it coerces
const y: *const usize = x; // just works
6 Likes
5

I was writing your exact snippet, but then realized he already used it for z

3 Likes
6

When I first time saw the @constCast function, I thought it will add the const modifier. :smiley:

Maybe @constToggle can be used in some generic functions. (I have not found any practical use cases though.)

1 Like
7

yeah, makes sense