enable_if and conversion operator?

Question

Any chance to use enable_if with a type conversion operator? Seems tricky, since both return type and parameters list are implicit.

Answer 1

Actually, I have found a way; we use a private, unused class to mark a conversion that shouldn't exist, and we use boost::mpl::if_ to select whether to produce a conversion to NoConversion, or to the desired type.

class A {
    class NoConversion { };
    template operator typename boost::mpl::if_::type() const;
}