Expected or Bug? struct range unmodified after foreach

[Jesse Phillips]

I'm sure if this was changed there would be other interesting behavior, 
such as arrays being consumed. And suggestions other than

    for(S s; !s.empty, s.popFront())...

Example:

    void main() {
        S s;

        foreach(i; s) {
            assert(i == s.popCount); // Fail
        }

        assert(s.popCount == 10); // Fail
    }

    struct S {
        size_t popCount;

        auto empty() {
            if(popCount > 9)
                return true;
            return false;
        }
        auto front() { return popCount; }
        auto popFront() {
            popCount++;
        }
    }