Description
A discussion in the Rust Lang BR Telegram channel raised a use case where the if guard in a match statement needed to call a split_at method and check one of the results while binding the other (IIRC). The context was that there was a desire to match a struct based on different fields, and in some cases on parts of one of the fields that was a slice.
Slice patterns were suggested as an alternative (an example was posted here: https://play.rust-lang.org/?gist=20432c8157a5bd5d560116a8d7bd4ab0&version=nightly), but we also brainstormed that it would be a nice feature if we could bind inside the guard condition. I suggested that it would be interesting to have an if let guard, that could work as follows:
match something {
// some initial cases
// ...
x if let (&[0, 1], tail) = x.split_at(2) => do_something_with(tail),
// other cases
// ..
_ => println!("No match"),
}
Which would be syntax sugar for something like:
match something {
// some initial cases
// ...
x => {
if let (&[0, 1], tail) = x.split_at(2) {
do_something_with(tail)
} else {
match x {
// other cases
// ...
_ => println!("No match"),
}
}
}
}
In case it's possible to have no _, i.e., the original match statement is exhaustive, then the generated code could include a _ => unreachable!("expected an exhaustive match case"); inside the inner match statement.