Pre-RFC: syntax sugar for `matches!`

language design
3
  • This was a placeholder for me while I still formulate my ideas, I have edited for clarity.

I'm imagining a situation similar to javascript's === vs ==, although the reasoning would be performance rather than correctness. Look at the following example:

fn src() -> Result<usize, usize> { /*...*/ }

fn foo() {
    if src() ~= Ok(0) {
        /* stuff */
    }
}

fn bar() {
    if src() == Ok(0) {
        /* stuff */
    }
}

If you view the MIR, foo has fewer memory accesses. I do not know MIR intimately, I do see that Bar creates 3 references and uses a promoted.