mirror of https://github.com/rust-lang/rust
49 lines
1.2 KiB
Rust
49 lines
1.2 KiB
Rust
#![feature(const_mut_refs)]
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#![feature(inline_const_pat)]
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use std::marker::PhantomData;
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#[derive(PartialEq, Eq)]
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pub struct InvariantRef<'a, T: ?Sized>(&'a T, PhantomData<&'a mut &'a T>);
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#[derive(PartialEq, Eq)]
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pub struct CovariantRef<'a, T: ?Sized>(&'a T);
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impl<'a, T: ?Sized> InvariantRef<'a, T> {
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pub const fn new(r: &'a T) -> Self {
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InvariantRef(r, PhantomData)
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}
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}
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impl<'a> InvariantRef<'a, ()> {
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pub const NEW: Self = InvariantRef::new(&());
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}
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impl<'a> CovariantRef<'a, ()> {
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pub const NEW: Self = CovariantRef(&());
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}
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fn match_invariant_ref<'a>() {
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let y = ();
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match InvariantRef::new(&y) {
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//~^ ERROR `y` does not live long enough [E0597]
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const { InvariantRef::<'a>::NEW } => (),
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}
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}
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fn match_covariant_ref<'a>() {
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// Unclear if we should error here (should we be able to subtype the type of
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// `y.0`), but using the associated const directly in the pattern also
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// errors.
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let y: (CovariantRef<'static, _>,) = (CovariantRef(&()),);
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//~^ ERROR lifetime may not live long enough
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match y.0 {
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const { CovariantRef::<'a>::NEW } => (),
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}
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}
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fn main() {
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match_invariant_ref();
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match_covariant_ref();
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}
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