Recursive shrink implementation requiring Clone on sub-iterators.

[burntsushi]

Recursive shrink implementation requiring Clone on sub-iterators.

[cristicbz]

I rattled my brain for the better part of a day, and of course the moment I file the issue I figure it out. This library is so cool, the solution is really simple for everyone seeing this in future:

fn shrink(&self) -> Box<Iterator<Item=Foo>> {
    Box::new((self.bar.clone(), self.baz.clone()).shrink().map(|(bar, baz)| Foo { bar: bar, baz: baz }))
}

Boom! Tuples FTW!

[BurntSushi]

Glad you got it figured out. Indeed, falling back to tuple implementations of Arbitrary is a key trick in the Haskell quickcheck library too. It is also useful when you want to test properties with more than four parameters (or otherwise add more impls of Testable, but that's a pain).

Using an associated type isn't really tenable, I think. As you said, you can't provide a default impl. More than that, it makes shrinkers tedious to write, because you have to write out the concrete iterator types, which is, in my experience, quite laborious.