mirror of https://github.com/rust-lang/rust
41 lines
944 B
Rust
41 lines
944 B
Rust
use std::ops::Deref;
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use std::rc::Rc;
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struct Value<T>(T);
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pub trait Wrap<T> {
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fn wrap() -> Self;
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}
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impl<R, A1, A2> Wrap<fn(A1, A2) -> R> for Value<fn(A1, A2) -> R> {
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fn wrap() -> Self {
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todo!()
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}
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}
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impl<F, R, A1, A2> Wrap<F> for Value<Rc<dyn Fn(A1, A2) -> R>> {
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fn wrap() -> Self {
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todo!()
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}
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}
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impl<F> Deref for Value<Rc<F>> {
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type Target = F;
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fn deref(&self) -> &Self::Target {
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&*self.0
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}
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}
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fn main() {
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let var_fn = Value::wrap();
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//~^ ERROR type annotations needed for `Value<Rc<_>>`
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// The combination of `Value: Wrap` obligation plus the autoderef steps
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// (caused by the `Deref` impl above) actually means that the self type
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// of the method fn below is constrained to be `Value<Rc<dyn Fn(?0, ?1) -> ?2>>`.
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// However, that's only known to us on the error path -- we still need
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// to emit an ambiguity error, though.
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let _ = var_fn.clone();
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}
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