Switching on pointers to tagged unions

Explain
1

Is there a reason for something like this to not be allowed?

const Value = union(enum) {
    int: i32,
    float: f32,
};

const v: Value = .{ .int = 10 };
const v_ptr = &v;
switch (v_ptr) {
    .int => |i| std.debug.print("int {d}", .{i}),
    .float => |f| std.debug.print("float: {d:.3}", .{f}),
    else => unreachable,
}
2

Because switch (v_ptr.*) { ... } achieves the same thing? :person_shrugging:

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3

Because switches act on the direct values, if given a pointer you will be comparing the address (yes, you can do this), not the dereferenced value.

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4

ty! switching on direct addresses seems kinda cursed lol but still cool

5

It’s more type safe to allow it than forcing to convert to an integer and switching on that, you’d lose the child type and constness doing that.

6

Unfortunately switching on pointers has been broken for quite a while on the LLVM backend (and I think also on some other backends):

and in light of #23509 it’s probably going to be removed anyway.

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