22 lines
661 B
Rust
22 lines
661 B
Rust
// compile-flags: -Znext-solver
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// check-pass
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fn map<T: Default, U, F: FnOnce(T) -> U>(f: F) {
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f(T::default());
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}
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fn main() {
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map::<i32, _ /* ?U */, _ /* ?F */>(|x| x.to_string());
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// PREVIOUSLY when confirming the `map` call, we register:
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//
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// (1.) ?F: FnOnce<(i32,)>
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// (2.) <?F as FnOnce<(i32,)>>::Output projects-to ?U
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//
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// While (1.) is ambiguous, (2.) immediately gets processed
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// and we infer `?U := <?F as FnOnce<(i32,)>>::Output`.
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//
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// Thus, the only pending obligation that remains is (1.).
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// Since it is a trait obligation, we don't use it to deduce
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// the closure signature, and we fail!
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}
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