Question

I have something like a sort-algorithm here, and I want to pass it a functor, which provides the sorting criteria (std::binary_function). So it should call T.operator<() for example if std::less is given.

Problem is, the member function operator() is not virtual. So I need to know which type of object was given, to perform a dynamic cast which is not really nice.

Regards,

Dennis

Answer 1

Problem is, the member function operator() is not virtual. So I need to know which type of object was given, to perform a dynamic cast which is not really nice.

Why do you want to perform a dynamic cast? Normally you don’t need that. Just call the functor’s operator() just like you would call a normal function.

The whole point of a functor is that they behave like normal functions and you’re passing a template parameter into your algorithm (aren’t you?) to handle different functor (and function) types.

Of course, this whole thing is predicated on the fact that you are actually passing a template parameter into your function. std::binary_function is not suited as a virtual base class. It merely exists to define a few handy typedefs. Thus, your function declaration should look like this:

template <typename TBinaryFunction>
void your_algorithm(rest of parameters …, TBinaryFunction f);