[Pre-Pre-RFC] Reviving Refutable Let [Runoff]

language design
4

I’d like to add another option to that list:

let match Variant0(x) = expr {
    Variant1(..) => ...,
    Variant2(..) => ...,
    ...
}
// `x` is in-scope here

I think this is preferable to let ... else for a couple of reasons. Firstly, it’s just as powerful since you can use a single match branch to blindly capture all possibilities other than the pattern you were looking for. eg:

let match Foo(x) = expr {
    _ => return,
}

Secondly, when you test to see whether expr matches your patten you’re already doing a match on it. So it makes sense to have access to the result of that match in the “else” clause. Otherwise people will end up writing code like this:

let Ok(x) = my_result else {
    let err = my_result.unwrap_err();    // ewww! unwrap!
    ...
}

Edit: Although maybe match let would be better than let match. That would make it look like if let and while let although that might be a bad thing since match let binds variables in the code after the block, not in the block.

12 Likes