no_std support

[perlindgren]

Hi Helgoboss

I came across your crate while looking to implement support for usb-midi in no_std context. Your crate looks great, and I think it could be very usable also for embedded applications. I tried to strip it from std dependencies, but there is no core::error (rust-lang/rust#33149).

So what's your take on this?

(There are some other crates for midi with no_std support, but none seems as elegant as yours.)

Best regards
Per Lindgren

[helgoboss]

Hi Per, glad you stumbled upon this crate and find it useful :) I would be happy to make this usable in a no_std context. Is the lack of core::error the only blocker you ran into?

I'm open to alternatives concerning the error types. Do you have any idea how this is usually handled in no_std crates? I just followed the rigorously the Rust API Guidelines (I think this in particular), therefore the current code.

[perlindgren]

Hi
I made a PR. There were a few dependencies that needed attention, but I got it to compile.

The main difference is that the newtype::new cannot use format! (I left the original code there commented out).

Especially in a no_std environment, "assert -> panic" is a bit problematic, perhaps new could return an Option (or even a Result). In any case the error is not local to new but rather a usage fault (you are trying to construct an illegal type).

Later one could think of a no_std (or std) as a feature, if you think there are some limitations to the no-default-features restriction on num_enum.

To be fair, I never used the core-error crate before, maybe there are other (better) options.

The tests pass, so I think you should be able to merge it as is.

/Per

[helgoboss]

Amazing, thanks for the PR. Will look into it.