1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
|
// Minimized case from typenum that didn't compile because:
// - We tried to normalize the ParamEnv of the second impl
// - This requires trying to normalize `GrEq<Self, Square<Square<U>>>`
// - This requires proving `Square<Square<U>>: Sized` so that the first impl
// applies
// - This requires Providing `Square<Square<U>>` is well-formed, so that we
// can use the `Sized` bound on `Mul::Output`
// - This requires proving `Square<U>: Mul`
// - But first we tried normalizing the whole obligation, including the
// ParamEnv, which leads to a cycle error.
// check-pass
trait PrivateSquareRoot {}
pub trait Mul<Rhs = Self> {
type Output;
}
pub trait IsGreaterOrEqual<Rhs> {
type Output;
}
pub type Square<A> = <A as Mul>::Output;
pub type GrEq<A, B> = <A as IsGreaterOrEqual<B>>::Output;
impl<A, B> IsGreaterOrEqual<B> for A {
type Output = ();
}
impl<U> PrivateSquareRoot for U
where
U: Mul,
Square<U>: Mul,
GrEq<Self, Square<Square<U>>>: Sized,
{
}
fn main() {}
|
