multiple inherit enable_shared_from_this

multiinherit_shared.cc

/* Trick to allow multiple inheritance of objects
 * inheriting shared_from_this.
 * cf. http://stackoverflow.com/a/12793989/587407
 */

/* First a common base class
 * of course, one should always virtually inherit from it.
 */
class MultipleInheritableEnableSharedFromThis: public std::enable_shared_from_this<MultipleInheritableEnableSharedFromThis>
{
public:
  virtual ~MultipleInheritableEnableSharedFromThis()
  {}
};

template <class T>
class inheritable_enable_shared_from_this : virtual public MultipleInheritableEnableSharedFromThis
{
public:
  std::shared_ptr<T> shared_from_this() {
    return std::dynamic_pointer_cast<T>(MultipleInheritableEnableSharedFromThis::shared_from_this());
  }
  /* Utility method to easily downcast.
   * Useful when a child doesn't inherit directly from enable_shared_from_this
   * but wants to use the feature.
   */
  template <class Down>
  std::shared_ptr<Down> downcasted_shared_from_this() {
    return std::dynamic_pointer_cast<Down>(MultipleInheritableEnableSharedFromThis::shared_from_this());
  }
};

class A: public inheritable_enable_shared_from_this<A>
{
public:
    void foo1()
    {
        auto ptr = shared_from_this(); 
    }
};

class B: public inheritable_enable_shared_from_this<B>
{
public:
    void foo2()
    {
        auto ptr = shared_from_this(); 
    }
};

class C: public inheritable_enable_shared_from_this<C>
{
public:
    void foo3()
    {
        auto ptr = shared_from_this(); 
    }
};

class D: public A, public B, public C
{
public:
    void foo()
    {
        auto ptr = A::downcasted_shared_from_this<D>(); 
    }
};