Cannot generate tuple-accession-syntax through macros

[qrlpx]

E.g. mytuple.0 can't be generated by mytuple.$num due to rust only accepting an identifier here. And digits ofc are expressions....

Minimal Example:

#![feature(macro_rules)]

macro_rules! nth(
    ($n:expr,$x:ident) => ($x.$n);
)

fn main(){
    let foo = (2u, 3u, 4u);
    let bar = nth!(2, foo);
}

[bluss]

The tuple module shows a way to work around it. http://doc.rust-lang.org/1.5.0/src/core/tuple.rs.html#39-57

[steveklabnik]

Traige: updated code

macro_rules! nth(
        ($n:expr,$x:ident) => ($x.$n);
        );

fn main(){
        let foo = (2, 3, 4);
            let bar = nth!(2, foo);
}

Given that there's a workaround and we're not doing significant work on current macros, I'm not sure this will ever be fixed.

[bluss]

From Rust 1.12 you can use the matcher tt for the tuple field index and use it directly in the macro expansion, without any "as_expr" ast coercion trick, so this is now fixed. (The matcher expr is not allowed.)

The working macro is:

macro_rules! nth {
    ($n:tt, $x:ident) => ($x.$n);
}