5.15 Summary

Using good libraries in C++ is (or at least ought to be) a lot easier than writing them. On the other hand, writing libraries is a lot of fun. Looking back at all the implementation details, there are a few lessons to keep in mind when writing generic code:

• When it comes to types, templatize and postpone. Be generic. FunctorHandler and MemFunHandler gain a lot from postponing type knowledge by using templates. Pointers to functions came for free. In comparison with what it offers, the codebase is remarkably small. All this comes from using templates and letting the compiler infer types as much as possible.

• Encourage first-class semantics. It would have been an incredible headache to operate only with FunctorImpl pointers. Imagine yourself implementing binding and chaining.

Clever techniques should be applied for the benefit of simplicity. After all this discussion on templates, inheritance, binding, and memory, we distill a simple, easy-to-use, well-articulated library.

In a nutshell, Functor is a delayed call to a function, a functor, or a member function. It stores the callee and exposes operator() for invoking it. Let's highlight some quick facts about it.