It's not a biggie, but was quite distracting for a few minutes

class IsOdd
{
public:
    int opCall()(int i)            // <== Not here
    {
        return 0 != (i % 2);    // <== Here!!
    }
};


This gives "test1.d(51): undefined identifier i", but the line indicated is the one inside the function, not the signature.

Weird. :)