`size_of_val_raw` is not a generalization of `size_of_val`

[maxdexh]

Location (URL)

https://doc.rust-lang.org/std/mem/fn.size_of_val_raw.html#safety

Summary

The safety requirements of size_of_val_raw state that conservatively, you are not allowed to call the function on anything other than T: Sized, [T], dyn Trait and ExternType (and types with unsized tail of these kinds).

But this means that even for pointers created from references, downstream code is not allowed to call the function in contexts where the pointee type is a generic T: ?Sized; it has to assume that there may be other kinds of types that don't fall into one of these cases.

This seems like an oversight.

@rustbot label T-libs T-lang

[theemathas]

@RalfJung

[Jules-Bertholet]

This is fixed in beta already #158893

[maxdexh]

Thanks! I could have sworn I was on the nightly site. I'll have to write a script to redirect me automatically at some point...