New API for using atoms

[rusterlium]

New API for using atoms

[jorendorff]

@scrogson pointed out that Rust keywords (like true and false) won't work with this kind of setup.

So here is another possible idea:

declare_atom_mod!(atoms {ok, ponies, true as true_atom, false as false_atom})

To use it, you would say atoms::ok(), atoms::true_atom(), etc.

[jorendorff]

Also - the current code for atom leaks an environment, types::atom::ATOM_ENV.

[jorendorff]

@hansihe Implemented this. The patch adds a bunch of functions types::atom::{ok, error, badarg, ...}

I decided on semicolons instead of commas because semicolons are usual for declarations, and trailing is better than separating. (Supporting an optional trailing comma in a Rust macro is weirdly hard.)

[hansihe]

Great work! What do you think about removing the old NIF creation functions? This way seems to be superior in almost every way.

[jorendorff]

Taking a look at that now...

[jorendorff]

OK, 82f30c8 is my attempt. It replaces the old functions with two new ones. Take a look.

[jorendorff]

Two quirks about rustler_atoms!:

• If you call it twice in the same scope, you get errors, because all the functions share a cache (by design) and we call it RUSTLER_ATOMS. There can't be two things with that name in the same scope.

• The functions it creates are all public. Nothing else in Rust is public by default.

I think these are acceptable. Or, we could change the macro to declare a module of functions, instead of just functions. That would address both issues, but it's a little wordier to use:

// Current design
rustler_atoms! {
    atom wine;
    atom cheese;
}

// Alternative design
rustler_atoms_mod! {
    mod france_atoms {  // module is private by default
        atom wine;  // seems ok for these to be public by default
        atom cheese;
    }
}
use self::france_atoms::*;

[OvermindDL1]

Could support both?

[hansihe]

Alternatively, atoms could have a pub modifier:

rustler_atoms! {
    pub atom wine;
    pub atom cheese;
}