Deprecate .as[A] method for decoding

[vkostyukov]

The .as[A] method should only be supported for HList => A conversion (through the Generic instance). As far as the API changes go, I see the following migration schema:

• param("foo").as[A] becomes param[A]("foo")
• Should we do the same for headers? How popular is that to read non-string values out of headers?

[sergeykolbasov]

Going to pick up this one if it's ok.

Just to make it clear: .as for HList => A should stay untouched, right?

[spockz]

Should we do the same for headers? How popular is that to read non-string values out of headers?

The only cases I know are authentication and.., just authentication.

[rpless]

Yes, iirc, .as for HList => A should stay the same. I think we should include headers with this, because would be a more consistent API and there are use cases for numbers and (maybe UUIDs) being in headers.

[vkostyukov]

Yeah, I guess the idea end state we want to be in is to keep as[Foo] as only a syntax extension for HList => Foo conversion.

I think I played with it in the past and turns out supporting a deprecation cycle would be a huge pain.

[vkostyukov]

Looks like we also need to add multipartAttribute to the list.

[vkostyukov]

I'm closing this for now as I'm not sure we have to wait for multipartAttribute to support a new pattern. The multipart* API is quite new and I think it's actually quite fine to wait a couple of more iterations before evolving it.