error.txt

tests/quickcheck.rs:126:20: 126:21 error: the type parameter `R` is not constrained by the impl trait, self type, or predicates [E0207]
tests/quickcheck.rs:126 impl<T: Arbitrary, R> Arbitrary for T where R: Default + Restriction<T> {

tests.rs

trait Restriction<T> {
    fn is_restricted(&mut self, x: &T) -> bool;
}

impl<T: Arbitrary, R> Arbitrary for T where R: Default + Restriction<T> {
    fn arbitrary<G: Gen>(g: &mut G) -> T {
        let restrictor = R::default();
        loop {
            let ret = T::arbitrary(g);
            if !restrictor.is_restricted(ret) {
                return ret;
            }
        }
    }
}