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  1. #include <iostream>
  2. #include <typeinfo> 
  3. #include <memory>
  4.  
  5. struct nil		{ };
  6.  
  7. //スマートポインタを生ポインタと同様に扱うための変換
  8. //int -> nil*,  int* -> int*,  smart_ptr<int> -> int*
  9. template <typename T>
  10. 	class dereferencable	{
  11. 		static T getT();
  12. 		template <typename U>
  13. 			static std::true_type test1(U&& u, decltype(*u, 0) = 0);	//本来はtest1だけでOKのはず
  14. 		template <typename U>
  15. 			static std::true_type test2(U&& u, typename std::enable_if<std::is_same<	//workaround for VC2012
  16. 								typename std::remove_cv<typename std::remove_reference<decltype(&*u)>::type>::type,
  17. 								typename std::remove_cv<typename std::remove_reference<decltype(&u)>::type>::type
  18. 										>::value>::type* = 0 );
  19. 		static std::false_type	test1(...);
  20. 		static std::false_type	test2(...);
  21. 		typedef decltype(test1(getT()))	T1;
  22. 		typedef decltype(test2(getT()))	T2;
  23. 		typedef typename std::conditional<T1::value && !T2::value, T, nil*>::type  psp_type; 
  24. 		static psp_type	getPSP();
  25. 	public:
  26. 		static const bool value = (T1::value && !T2::value);	//int -> false,  int* -> true,  s_ptr<int> -> true
  27. 		typedef decltype(&*getPSP())	p_type;		//int -> nil*,  int* -> int*,  s_ptr<int> -> int*
  28. 	};
  29.  
  30.  int  main()
  31. {
  32. 	int v=9;
  33. 	int* p = &v;
  34. 	std::unique_ptr<int> sp(new int(14312421));
  35.  
  36. 	std::cout << dereferencable<decltype(v)>::value << std::endl;
  37. 	std::cout << dereferencable<decltype(p)>::value << std::endl;
  38. 	std::cout << dereferencable<decltype(sp)>::value << std::endl;
  39.  
  40. 	std::cout << typeid(nil*).name() << " : " <<
  41. 		typeid(dereferencable<decltype(v)>::p_type).name() << std::endl;
  42. 	std::cout << typeid(int*).name() << " : " <<
  43. 		typeid(dereferencable<decltype(p)>::p_type).name() << std::endl;
  44. 	std::cout << typeid(int*).name() << " : " <<
  45. 		typeid(dereferencable<decltype(sp)>::p_type).name() << std::endl;
  46.  
  47.  
  48. 	return 0;
  49. }
Success #stdin #stdout 0s 3428KB
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P3nil : P3nil
Pi : Pi
Pi : Pi
https://ideone.com/k1cPey
language:
C++14 (gcc 8.3)
created:
11 years ago
visibility:
public

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