Question

I have a class test which isn’t standard constructable nor assignable due to certain reasons. However it is copy constructable – on may say it behaves a bit like a reference.

Unfortunately I needed a dynamic array of these elements and realized that vector<test> isn’t the right choice because the elements of a vector must be standard constructable and assignable. Fortunately I got around this problem by

• using vector<T>::reserve and vector<T>::push_back instead of vector<T>::resize and direct filling the entries (no standard construction)

• the copy’n’swap trick for assignment and the fact that a vector is usually implemented using the Pimpl-idiom (no direct assignment of an existing test element), i.e

  class base {
  private:
      std::vector<test> vect;
      /* ... */
  public:
      /* ... */
      base& operator= (base y) {
          swap(y);
          return *this;
      }
      void swap(base& y) {
          using std::swap;
          swap(vect, y.vect);
      }
     /* ... */
  };
  

Now I assume that I probably didn’t considered every tiny bit and above all these tricks are strongly implementation dependent. The standard only guarantees standard behavior for standard constructable and assignable types.

Now what’s next? How can I get a dynamic array of test objects?

Remark: I must prefer built in solutions and classes provided by the standard C++.

Edit: I just realized that my tricks actually didn’t work. If I define a really* non assignable class I get plenty of errors on my compiler. So the question condenses to the last question: How can I have a dynamic array of these test objects?

(*) My test class provided an assignment operator but this one worked like the assignment to a reference.

Answer 1

Edit: The below is no longer good practice. If your object supports moving then it will probably fit into a vector (see the std::vector elements requirements for details, in particular the changes for C++17).

Consider using Boost’s ptr_vector, part of the Boost Pointer Container Library. See in particular advantage #3 in that library’s motivation.