Exceptional C++ Style 40 New Engineering Puzzles, Programming Problems, and Solutions

Chapter 8. Befriending Templates

Difficulty: 4

If you want to declare a function template specialization as a friend, how do you do it? According to the C++ standard, you can choose either of two legal syntaxes. According to real-world compilers, however, one of the syntaxes is widely unsupported; the other works on all current versions of popular compilers… except one.

Let's say we have a function template that does SomethingPrivate to the objects it operates on. In particular, consider the boost::checked_delete function template from [Boost], which deletes the object it's given—among other things, it invokes the object's destructor:

namespace boost {
 template<typename T> void checked_delete(T* x) {

  // … other stuff …

  delete x;
 }
}

Now, say you ...