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

Chapter 6. Flavors of Genericity, Part 2: Generic Enough?

Difficulty: 7

How generic is a generic function, really? The answer can depend as much on its implementation as on its interface, and a perfectly generalized interface can be hobbled by simple—and awkward-to-diagnose—programming lapses.

Guru Question

1. There is a subtle genericity trap in the following functions. What is it, and what's the best way to fix it?

   template <class T>
   void destroy(T* p) {
    p->~T();
   }
   
   template <class FwdIter>
   void destroy(FwdIter first, FwdIter last) {
    while(first != last) {
     destroy(first);
     ++first;
    }
   }
   

2. What are the semantics of the following function, including the requirements on T? Is it possible to remove any of those requirements? If so, demonstrate how, and argue ...