If a match expression has one arm that returns a borrowed matched value from its pattern, and another arm that doesn't borrow directly from a matched value but instead borrows the variable the matched value borrows and returns it, compilation fails if the match statement is returning from a function, but not if it's assigning to a variable. This used to work (and iirc one of the goals of NLLs was to make this pattern work), but it broke between nightly-2018-05-17 and nightly-2018-05-19. A nightly for May 18th doesn't appear to exist.
Examples:
This doesn't work now:
// Doesn't compile on nightly-2018-05-19 and later, but does on nightly-2018-05-17.
fn borrow(o: &mut Option<i32>) -> Option<&mut i32> {
match o.as_mut() {
Some(i) => Some(i),
None => o.as_mut()
}
}
This is similar to the other code, but does work both before and after nightly-2018-05-19
fn main() {
let mut o: Option<i32> = Some(1i32);
// Compiles everywhere!
let x = match o.as_mut() {
Some(i) => Some(i),
None => o.as_mut()
};
}
schneiderfelipe, tuguzT, emadpres, Millione, SimonMaracine and 1 more
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