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