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