76 lines
1.7 KiB
Rust
76 lines
1.7 KiB
Rust
// 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 { ... }`
|
|
|
|
|
|
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)));
|
|
}
|
|
}
|