Feature: Repeat index in macros

[Centril]

It would be really swell if you could somehow access the index or depth of the current repeat in a macro.

Say if we are repeating with $($x), then $#x would yield the index of the current $x in the sequence.

The $# is really not important, could be anything else really.

For example:

#[macro_export]
macro_rules! letmany {
    ($($x:ident),+) => {
        let $x = $#x;
    };
}

fn main() {
    letmany!(a, b, c);
}

Would expand to:

fn main() {
    let a = 0;
    let b = 1;
    let c = 2;
}

Thoughts?

[lilyball]

As mentioned on IRC, this has already been filed as #12782 and #12916, and in both cases the decision was that this has to go through the RFC process. I filed an RFC that covered this as rust-lang/rfcs#88, which has lots of discussion, and the ultimate decision was that this is a post-1.0 feature.

If you have any feedback on this, commenting on that RFC is probably the best bet, as that's likely to be the starting point for any further discussion of this post-1.0.

[Centril]

Thanks, I'll close this issue and comment on the RFC instead.