The notion of ownership

When we say that object Aowns object B, what we mean is that object A manages the lifetime of object B--that A controls the construction, copying, moving, and destruction of object B. The user of object A can (and should) "forget about" managing B (for example, via explicit calls to delete B, fclose(B), and so on).

The simplest way for an object A to "own" an object B is for B to be a member variable of A. For example:

    struct owning_A {
      B b_;
    };

    struct non_owning_A {
      B& b_;
    };

    void test()
    {
      B b;

      // a1 takes ownership of [a copy of] b.
      owning_A a1 { b };

      // a2 merely holds a reference to b;
      // a2 doesn't own b.
      non_owning_A a2 { b };
    }

Another way is for A to hold a pointer to B, with the appropriate code in ~A() (and, if necessary, in the copy and move operations of A) to clean up the resources associated with that pointer:

    struct owning_A {
      B *b_;

      explicit owning_A(B...