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// Taken from https://github.com/rust-lang/rust/blob/6cc0a764e082d9c0abcf37a768d5889247ba13e2/compiler/rustc_typeck/src/check/_match.rs#L445-L462
//
// We attempt to `let Bar::Present(_) = foo else { ... }` where foo is meant to Deref/DerefMut to
// Bar. This fails, you must add a type annotation like `let _: &mut Bar = _ else { ... }`
#![feature(let_else)]
use std::ops::{Deref, DerefMut};
struct Foo(Bar);
enum Bar {
Present(u32),
Absent,
}
impl Deref for Foo {
type Target = Bar;
fn deref(&self) -> &Bar {
&self.0
}
}
impl DerefMut for Foo {
fn deref_mut(&mut self) -> &mut Bar {
&mut self.0
}
}
impl Bar {
fn bar(&self) -> Option<u32> {
let Bar::Present(z): &Bar = self else {
return None;
};
return Some(*z);
}
}
impl Foo {
// Try without the type annotation
fn set_bar_unannotated(&mut self, value: u32) {
let Bar::Present(z) = self else { //~ ERROR mismatched types
return;
};
*z = value;
}
}
fn main() {
let mut foo = Foo(Bar::Present(1));
foo.set_bar_unannotated(54);
assert_eq!(foo.bar(), Some(54));
irrefutable::inner();
}
// The original, to show it fails for irrefutable let decls
mod irrefutable {
use std::ops::{Deref, DerefMut};
struct Foo(Bar);
struct Bar(u32);
impl Deref for Foo {
type Target = Bar;
fn deref(&self) -> &Bar {
&self.0
}
}
impl DerefMut for Foo {
fn deref_mut(&mut self) -> &mut Bar {
&mut self.0
}
}
fn foo(x: &mut Foo) {
let Bar(z) = x; //~ ERROR mismatched types
*z = 54;
assert_eq!((x.0).0, 54);
}
pub fn inner() {
foo(&mut Foo(Bar(1)));
}
}
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