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Relate existential associated types with variance Invariant
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src/test/ui/variance/variance-associated-types2.nll.stderr
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error: lifetime may not live long enough | ||
--> $DIR/variance-associated-types2.rs:13:12 | ||
| | ||
LL | fn take<'a>(_: &'a u32) { | ||
| -- lifetime `'a` defined here | ||
LL | let _: Box<dyn Foo<Bar = &'a u32>> = make(); | ||
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^ type annotation requires that `'a` must outlive `'static` | ||
| | ||
= help: consider replacing `'a` with `'static` | ||
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error: aborting due to previous error | ||
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// Test that dyn Foo<Bar = T> is invariant with respect to T. | ||
// Failure to enforce invariance here can be weaponized, see #71550 for details. | ||
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trait Foo { | ||
type Bar; | ||
} | ||
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fn make() -> Box<dyn Foo<Bar = &'static u32>> { | ||
panic!() | ||
} | ||
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fn take<'a>(_: &'a u32) { | ||
let _: Box<dyn Foo<Bar = &'a u32>> = make(); | ||
//~^ ERROR mismatched types [E0308] | ||
} | ||
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fn main() {} |
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error[E0308]: mismatched types | ||
--> $DIR/variance-associated-types2.rs:13:42 | ||
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LL | let _: Box<dyn Foo<Bar = &'a u32>> = make(); | ||
| ^^^^^^ lifetime mismatch | ||
| | ||
= note: expected trait object `dyn Foo<Bar = &'a u32>` | ||
found trait object `dyn Foo<Bar = &'static u32>` | ||
note: the lifetime `'a` as defined on the function body at 12:9... | ||
--> $DIR/variance-associated-types2.rs:12:9 | ||
| | ||
LL | fn take<'a>(_: &'a u32) { | ||
| ^^ | ||
= note: ...does not necessarily outlive the static lifetime | ||
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error: aborting due to previous error | ||
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For more information about this error, try `rustc --explain E0308`. |