Error code E0657

An impl Trait captured a higher-ranked lifetime, which is not supported.

Currently, impl Trait types are only allowed to capture lifetimes from their parent items, and not from any for<'a> binders in scope.

Erroneous code example:

#![allow(unused)] fn main() { trait BorrowInto<'a> { type Target; fn borrow_into(&'a self) -> Self::Target; } impl<'a> BorrowInto<'a> for () { type Target = &'a (); fn borrow_into(&'a self) -> Self::Target { self } } fn opaque() -> impl for<'a> BorrowInto<'a, Target = impl Sized + 'a> { () } }