E0657 - Error codes index
Description: Book listing all Rust error codes

# 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> {
        ()
    }
    }