Broken findLast() function

findLast.swift

func findLast<C : Swift.Collection where C.GeneratorType.Element : Equatable>(domain: C, value: C.GeneratorType.Element) -> C.IndexType? {
    return reduce(enumerate(domain), nil) { (prevIndex: C.IndexType?, pair: (index: C.IndexType, elem: C.GeneratorType.Element)) -> C.IndexType? in
        if pair.elem == value {
            return pair.index
        }
        else {
            return prevIndex
        }
    }
    // It doesn't like the combine (closure) parameter:
    // 'Int' is not a subtype of 'C.IndexType'
    // But this function never mentions Int!
}

Update: Turns out that enumerate() numbers the elements with Ints, not the indices that actually appear in the collection.

That's a useful behavior.