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trait Foo<A> {
fn get(&self, A: &A) { }
}
trait Bar {
type Out;
}
impl<T> Foo<T> for [isize;0] {
// OK, T is used in `Foo<T>`.
}
impl<T,U> Foo<T> for [isize;1] {
//~^ ERROR the type parameter `U` is not constrained
}
impl<T,U> Foo<T> for [isize;2] where T : Bar<Out=U> {
// OK, `U` is now constrained by the output type parameter.
}
impl<T:Bar<Out=U>,U> Foo<T> for [isize;3] {
// OK, same as above but written differently.
}
impl<T,U> Foo<T> for U {
// OK, T, U are used everywhere. Note that the coherence check
// hasn't executed yet, so no errors about overlap.
}
impl<T,U> Bar for T {
//~^ ERROR the type parameter `U` is not constrained
type Out = U;
// Using `U` in an associated type within the impl is not good enough!
}
impl<T,U> Bar for T
where T : Bar<Out=U>
{
//~^^^ ERROR the type parameter `U` is not constrained
// This crafty self-referential attempt is still no good.
}
impl<T,U,V> Foo<T> for T
where (T,U): Bar<Out=V>
{
//~^^^ ERROR the type parameter `U` is not constrained
//~| ERROR the type parameter `V` is not constrained
// Here, `V` is bound by an output type parameter, but the inputs
// are not themselves constrained.
}
impl<T,U,V> Foo<(T,U)> for T
where (T,U): Bar<Out=V>
{
// As above, but both T and U ARE constrained.
}
fn main() { }
|
