WIP: Specialization of decoding for Bytes

[vorner]

I don't know if I understood #31 suggestion correctly, so I'd like to ask about it. I think it could work somehow like this:

• There would be a special method for decoding from bytes, that would default to just decoding from Buf.
• Generated Message instances would implement it similar as they implement the basic decoding.
• While most values can use the default, the newly supported Bytes would get a specialization and just use the part of the original buf.

While this probably would work, the in here looks like a big kludge to me. So did you have something else in mind?

I guess specialization (or how the feature is called) would greatly help, but it's not coming soon into Rust, is it?

[danburkert]

@vorner there shouldn't be a special method on Message for decoding from Bytes; specialization makes that unnecessary. To expand on the second bullet point in #31 specifically, there should be a new trait for string and bytes fields which allows for specialized decoding when the input buffer is a Bytes. That way you shouldn't need to change the call sites doing decoding at all, it should 'just work' as long as the message type has zero-copy configured fields, and the buffer is a Bytes instance.

[vorner]

I'm probably having some kind of mental roadblock here 😇

Specialization: you mean this one, that's still nightly only? rust-lang/rust#31844 Or is there anything else I'm missing? A very small example would probably be enough for me and I'd take it the rest of the way to implement it on everything that needs it.

[danburkert]

Closing this out per the comment I left in #31, please feel free to file a new issue if the solution in master doesn't work for you. Thanks!