RFC: Deserializing to a stream of tagged values

[erickt]

This is an RFC to convert Rust's deserialization framework to produce a stream of tagged values.

[kud1ing]

One less "into a".

[erickt]

@kud1ing: Fixed, thanks.

[erickt]

For reference, I have an experimental repository that implements many of these ideas: https://github.com/erickt/rust-serde. I made it a couple months ago, so it does not run against rust HEAD at the moment.

[erickt]

I've updated https://github.com/erickt/rust-serde to with with Rust HEAD, assuming rust-lang/rust#14120 lands.

@BurntSushi: you expressed interest in playing around with it. I still have some modernization to do on it though.

[nikomatsakis]

@erickt some scattered thoughts:

1. I am confused by the premise of this RFC. We currently include the ability to handle enums, which basically amounts to serializing an integer and then doing a match inside the decoder?
2. In general, I like the approach, but I'd be happier if the stream of tagged values were somehow more primitive. For example, just ints/uints/chars and "tags", and maybe we define some standard tags for grouping. I'm wary of decoders that require lookahead though.
3. Performance is pretty important. I'd like to convert rustc to use the standard encoders/decoders but my last effort (admittedly some time ago) led to a rather large drop in compile-times, so I never landed it.
4. Have you compared with other existing efforts to make standard serializers and deserializers? I'm not sure what we can learn from there, if anything.
5. As a meta-thought, I do think the encodable/decodable need work but -- when I last investigated -- I found some other type system problems holding up proper resolution. Unfortunately I haven't made much progress in resolving those, I'll give it a shot.

[mhristache]

Is this suppose to offer a solution for rust-lang/rust#12794?

[erickt]

@TheMax: yes this will be able to handle #12794. I've already implemented support for it in https://github.com/erickt/rust-serde.

[aturon]

I'm going to close this RFC for now, since these ideas are embodied in @erickt's serde library. While this may eventually become part of std, for now it lives out of tree.