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Disregard: Broken attempt at type_id hack on stable Rust with no unsafe #139043
Description
[Edit: Removed a bunch of things that don't matter because this doesn't do what was intended:]
use core::{any::TypeId, marker::PhantomData};
fn type_id_of<T: ?Sized>() -> TypeId {
trait Marker {}
impl<T: ?Sized> Marker for T {}
fn hack<T: ?Sized + Marker + 'static>(_: *const T) -> TypeId {
TypeId::of::<T>()
}
let p = &PhantomData::<T>;
let p = &raw const *p as *const (dyn Marker + 'static);
hack(p)
}
fn type_id_of_val<T: ?Sized>(_: &T) -> TypeId {
type_id_of::<T>()
}
fn main() {
let x = ();
dbg!(type_id_of_val(&x));
}
Activity
compiler-errors commentedon Mar 28, 2025
@traviscross:
All this code does is compute the type id of the type
dyn Marker + 'static. It's not violating any sort of library UB. https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=6a90175675c2021bf4f385714a3507a1What exactly are you trying to demonstrate in this code?
compiler-errors commentedon Mar 28, 2025
Also @traviscross could you please quit tagging approximately everyone in the world and then editing away those tags as soon as someone comments? It's pretty disruptive 😅
traviscross commentedon Mar 28, 2025
OK, thanks for that. One moment, I went too far in trying to simplify the example, but I may still have a version that works.
traviscross commentedon Mar 28, 2025
No, never mind. I thought I had something, but it doesn't work. Obviously have been staring at this too long. Sorry for the noise.
[-]`type_id` hack on stable Rust with no unsafe[/-][+]Broken attempt at `type_id` hack on stable Rust with no unsafe[/+][-]Broken attempt at `type_id` hack on stable Rust with no unsafe[/-][+]Disregard: Broken attempt at `type_id` hack on stable Rust with no unsafe[/+]