Tracking issue for type_id stabilization

[aturon]

The method get_type_id in Any is intended to support reflection. It's currently unstable in favor of using an associated constant instead.

[bluss]

It was pointed out it's one of the very few methods to be named with get_ prefix, so it could be renamed to just type_id().

[aturon]

I suspect this is just some very old convention that wasn't updated during stabilization (since we didn't stabilize this API).

[flosse]

Any progress here?

[UserAB1236872]

I tried to tackle it, but it looks like the main problem is that TypeId::of isn't constant and can't be constant. It calls intrinsics::type_id which, on any attempt to make it a const function yields the cryptic error "unmatched visibility pub". This would be a simple change if TypeId::of was a const fn.

(Though making an extern function const is probably dicey from a compiler perspective anyway, I'm not an expert on that).

[alexcrichton]

Removing nomination as this was an accidental mistake about what this issue was about.

[fschutt]

Any update on this? Is is discouraged to use it in current code?

[jweinst1]

Is there any other way to do reflection or dynamic typing that will work?

[SimonSapin]

@jweinst1 the rest of the std::any::Any trait is stable:

fn is<T>(&self) -> bool where T: Any;
fn downcast_ref<T>(&self) -> Option<&T> where T: Any;
fn downcast_mut<T>(&mut self) -> Option<&mut T> where T: Any;
fn downcast<T>(Box<self>) -> Result<Box<T>, Box<Any>> where T: Any ;

In each of these the call site is specifying a specific T. (Internally the implementations of these method compare Self::type_id() and T::type_id().)

[SimonSapin]

I’ve just realized that TypeId and TypeId::of are also stable, so you could copy the Any trait into your own code.