auto-impl: parser support by dingxiangfei2009 · Pull Request #149335 · rust-lang/rust (original) (raw)

It's probably more a language-related comment, than compiler-related, but the placement of auto impls doesn't seem right.

Auto impls are not associated items, they could very well live as free items, and placed into the traits just for the proximity.
Ideologically it would be similar if we supported placing inherent impls for structs into the struct body, C++ style (which is requested sometimes). We do not do that to support separation of data and implementation, here it would make sense to support separation of interfaces and implementation as well.
There are many comments on the RFC, so I'm not sure if it was already discussed.

Even from the compiler point of view in HIR and below we'd now need to separate real associated items from the things that just live there in source code, and may break some other assumptions across the compiler about only one level of associated item nesting existing, making building the prototype harder.