Macros should have an operator type

[rust-highfive]

Issue by darkf
Thursday Aug 29, 2013 at 11:55 GMT

For earlier discussion, see rust-lang/rust#8853

This issue was labelled with: A-syntaxext, I-enhancement in the Rust repository

---

AFAIK there is currently no way to quote an operator such as + or /, and this would be useful to reduce code duplication.

Something like:

macro_rules! foo(
    ($oper:op) => 10i $oper 20i
)

fn main() {
    printfln!("%d", foo!(+));
    printfln!("%d", foo!(*));
}

[brendanzab]

Might be better to call it binop...? At the moment I just use the operator trait method names...

[saskenuba]

+1, this is really useful and would avoid a lot of boilerplate especially in operator overloading on simple structs

[petrochenkov]

tt can be used for passing a single token.

macro_rules! foo {
    ($oper:tt) => (10 $oper 20)
}

fn main() {
    println!("{}", foo!(+));
    println!("{}", foo!(*));
}

It won't reject non-operators though.

[glittershark]

tt can be used for passing a single token.

That doesn't work in all places an operator can exist, unfortunately, since eg expr can't be followed by tt:

macro_rules! example {
    ($lhs:expr $op:tt $rhs:expr) => {}
}

error: `$lhs:expr` is followed by `$op:tt`, which is not allowed for `expr` fragments
 --> src/main.rs:7:16
  |
7 |     ($lhs:expr $op:tt $rhs:expr) => {}
  |                ^^^^^^ not allowed after `expr` fragments
  |
  = note: allowed there are: `=>`, `,` or `;`

[kennytm]

$:expr can't be followed by a +, let alone any binary operator.

error: `$lhs:expr` is followed by `+`, which is not allowed for `expr` fragments
 --> src/lib.rs:2:16
  |
2 |     ($lhs:expr + $rhs:expr) => {}
  |                ^ not allowed after `expr` fragments
  |
  = note: allowed there are: `=>`, `,` or `;`

[glittershark]

oh wow, ok. Probably a separate rfc for that, in that case

[kennytm]

there is no way to "fix" this because example!(1 + 2 + 3 + 4) is a thing.