More Exceptional C++

Chapter 4. Extensible Templates: Via Inheritance or Traits?

Difficulty: 7

This Item reviews traits templates and demonstrates some cool traits techniques. Even without traits, what can a template figure out about its type—and what can it do about it? The answers are nifty and illuminating, and not just for people who write C++ libraries.

1. What is a traits class?

2. Demonstrate how to detect and make use of template parameters' members, using the following motivating case: You want to write a class template C that can be instantiated only on types that have a const member function named Clone() that takes no parameters and returns a pointer to the same kind of object.

   // T must provide T* T::Clone() const
   template<typename T>
   class C
   {
     // ...
   };
   

   Note: ...