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  1. #include<memory>
  2. #include<iostream>
  3. #include<typeinfo>
  4. using namespace std;
  5.  
  6. template<typename T>
  7. struct void_ { typedef void type; };
  8.  
  9. template<typename T, typename = void>
  10. struct My_sfinae {
  11.   typedef T RealType;
  12.   static T& getPtr (T &p) { return p; }
  13. };                        //^^^^^^^^^ business logic!
  14. template<typename T>
  15. struct My_sfinae<T, typename void_<typename T::smart_type>::type> {
  16.   typedef typename My_sfinae<typename T::smart_type>::RealType RealType;
  17.   static RealType& getPtr (T &p) { return My_sfinae<typename T::smart_type>::getPtr(p.getPtr()); }
  18. };
  19.  
  20. template<typename T>
  21. class some_smart_ptr_wrapper
  22. {
  23.   T m_ptr;
  24. public:
  25.   typedef T smart_type;  // <-- unique name
  26.   T& getPtr () { return m_ptr; }
  27.  
  28.   typename My_sfinae<T>::RealType& getFinalPtr () { return My_sfinae<T>::getPtr(m_ptr); }
  29. };
  30.  
  31. int main ()
  32. {
  33.   shared_ptr<int> p1; 
  34.   some_smart_ptr_wrapper<some_smart_ptr_wrapper<some_smart_ptr_wrapper<shared_ptr<int>>>> p2; 
  35.  
  36.   if(typeid(p1) == typeid(p2.getFinalPtr()))
  37.     cout << "working\n";
  38.   else
  39.     cout << "not working\n";
  40. } 
  41.  
Success #stdin #stdout 0s 2928KB
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working
https://ideone.com/8RBPU
language:
C++14 (gcc 8.3)
created:
11 years ago
visibility:
public

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