More Exceptional C++

Chapter 31. Smart Pointer Members, Part 2: Toward a ValuePtr

Difficulty: 6

Can we make life safer for ourselves and our users by devising a smart pointer class designed specifically for class membership?

1. Write a suitable ValuePtr template that is used as shown here:

   // Example 31-1
   //
   class X
   {
     // ...
   private:
     ValuePtr<Y> y_;
   };
   

   to suit three specific circumstances:

   1. Copying and assigning ValuePtrs is not allowed.

   2. Copying and assigning ValuePtrs is allowed and has the semantics of creating a copy of the owned Y object using the Y copy constructor.

   3. Copying and assigning ValuePtrs is allowed and has the semantics of creating a copy of the owned Y object, which is performed using a virtual Y::Clone() method if present and the Y copy constructor otherwise. ...