Thread: functional derivation better?

In that example, there is no difference at all, reason is... std::binary_function is never used...

Originally Posted by CodeMonkey

I'm told that if I derive my comparison function objects from std::binary_function, I'm "helping the STL." How? What does, std::sort(), for example, deduce from that template?

It gives the typedefs: first_argument_type, second_argument_type, result_type.

In theory, the STL (or your own algorithms even) might have some partial or complete specialization of an algorithm based on the specific types being passed to a functor. This information COULD be carried around as template type parameters, but this is unwieldy. It would force the user programmer to explicitly indicate the types for every instantiation of an object which acts like a binary function, even though the vast majority of algorithms don't make use of this information.


You also need the result_type if you want boost::bind to work correctly with your function object. You could define this yourself (and I have), but you could just as well derive from binary_function.