use serde instead of rustc_serialize

[tatref]

I wanted to tackle simias/rustation#38, and I thought I'd try on a smaller projet first, so here is a conversion from rustc_serialize to serde.

The only trouble is the following, I had to use a macro to serialize the data field.
I could validate a full serialize/deserialize cycle, because the ROMs I tried panicked with: Unhandled CUE pregap read

Let me know what you think about this PR

[simias]

Sorry for taking so long to review this, I hadn't checked my github in a while. I'll be sure to look into it in the following days.

Thank you for your interest at any rate!

[simias]

As far as the code is concerned it looks great to me. I'm slightly annoyed that we still have to use hackery to serialize big arrays but I guess it can't be helped in the current state of Rust and the custom derive is definitely more elegant than my solution.

Do you think the "big array" trait/macro will have to be replicated in every repositories or can it be centralized somewhere? Is it available in some 3rd party crate somewhere?

I couldn't get the full emulator to compile since RustcEncodable/Decodable doesn't seem to be compatible with Serde, I get errors like:

35 | #[derive(RustcDecodable, RustcEncodable)]
   |          ^^^^^^^^^^^^^^ the trait `rustc_serialize::Decodable` is not implemented for `cdimage::sector::Sector

How did you work around this?

Sorry again for taking so much time to look into this.

[tatref]

Hi,

First off, don't be sorry for taking your time!

Unfortunately, yes, the "big array" hack is still required (as long as the const generics are implemented). I couldn't find it on crates.io, but it would be interesting to put it on a dedicated repository.

The rustc and serde traites are not compatible, all the rustc part of the emulator must be rewritten... I tried it, be couldn't finish it properly. I have issues with the callback! macro, and also some Decodable implemetation that decode multiples fields in one single go.

Thanks for your answer!

[simias]

Ah I see, I misunderstood your original comment and thought you had managed to get the full emulator running.

So yeah this patch looks great to me but obviously its use is limited as long as the rest of the emulator is ported to serde. Can you maybe submit a PR of your work-in-progress for the rest of the emulator? I could have a look at it and see what can be done.

Regarding the callback! macro as you probably figured out it's just a workaround to be able to serialize function pointers. One possibility would be to get rid of function pointers altogether and instead dispatch the call with a match on some enum state machine. On a modern architecture it might actually end up being faster than the indirect branching too...