Miss Dada  🏳️‍⚧️

well, to be precise, it implements it for one type: `dyn Other`. &dyn Other, Box<dyn other> get it through deref, but they do not get the trait implemented

Box<dyn Other> and &dyn Other are not T: Other, as I mentioned before. They get Other methods through deref. Some traits (eg. Fn*) may choose to blanket implement themselves on these types.

dyn Other is a single type. It's a virtually dispatched trait object, with a concrete value of *some* type implementing that trait behind it. It can only exist behind a pointer, because we don't know its size.

"virtually" == dispatch is done at runtime?

Yes. It points to a vtable with the size information and function pointers to all the trait methods

but a `dyn Trait` cannot exist as a value on its own? it needs a wrapper type to implement a pointer to the concrete value?

Correct. Something has to actually point to that vtable and size information.

the thing I wasn't getting is that I was thinking about dynamic OO languages, where the class/vtable pointer is part of the value whereas here you have a pair of pointers, one to the value and one to the vtable that's relevant at that call site, it's contextual