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  1. #include <iostream>
  2.  
  3. struct bar;					// forward declaration
  4.  
  5. class foo {					// implicitly private
  6. 	friend struct ::bar;	// but bar is a friend
  7.  
  8. 	template<typename T = int>
  9. 	static void static_function_template() {}
  10.  
  11. 	template<typename T = int>
  12. 	void function_template() {}
  13.  
  14. 	template<typename T = int>
  15. 	class class_template {
  16. 		static void static_function() {}
  17. 		void function() {}
  18. 		static T static_value;
  19. 		T value;
  20. 	};
  21.  
  22. };
  23.  
  24. struct bar {				// implicitly public
  25.  
  26. 	// some alias templates referring to class foo:
  27. 	template<typename T> using type01 = decltype(foo::static_function_template<T>());
  28. 	template<typename T> using type02 = decltype(foo::static_function_template<>());
  29. 	template<typename T> using type03 = decltype(foo::static_function_template<T>);
  30.  
  31. 	template<typename T> using type04 = decltype(foo().function_template<T>());
  32. 	template<typename T> using type05 = decltype(foo().function_template<>());
  33.  
  34. 	template<typename T> using type06 = decltype(foo::class_template<T>::static_function());
  35. 	template<typename T> using type07 = decltype(foo::class_template<>::static_function());
  36. 	template<typename T> using type08 = decltype(foo::class_template<T>::static_function);
  37.  
  38. 	template<typename T> using type09 = decltype(foo::class_template<T>().function());
  39. 	template<typename T> using type10 = decltype(foo::class_template<>().function());
  40.  
  41. 	// check (has direct access to bar)
  42. 	template<template<typename> class TT, typename T, typename = TT<T>>
  43. 	static void check(int) { std::cout << "> can be instantiated       "; }
  44. 	template<template<typename> class TT, typename T>
  45. 	static void check(...) { std::cout << "> can NOT be instantiated   "; }
  46. };
  47.  
  48. // check (has no direct access to bar)
  49. template<template<typename> class TT, typename T, typename = TT<T>>
  50. void check(int) { std::cout << "> can be instantiated       "; }
  51. template<template<typename> class TT, typename T>
  52. void check(...) { std::cout << "> can NOT be instantiated   "; }
  53.  
  54.  
  55.  
  56. int main() {
  57. #ifdef __clang__
  58. 	std::cout << "-- compiled with clang --" << std::endl;
  59. #endif
  60. #ifdef _MSC_VER
  61. 	std::cout << "-- compiled with MSVC --" << std::endl;
  62. #endif
  63. #ifdef __GNUC__
  64. 	std::cout << "-- compiled with GCC --" << std::endl;
  65. #endif
  66. 	std::cout << std::endl;
  67.  
  68. 	std::cout << "         inside of bar:              outside of bar:             " << std::endl;
  69. 	std::cout << "type01   "; bar::check<bar::type01, int>(0); check<bar::type01, int>(0); std::cout << std::endl;
  70. 	std::cout << "type02   "; bar::check<bar::type02, int>(0); check<bar::type02, int>(0); std::cout << std::endl;
  71. 	std::cout << "type03   "; bar::check<bar::type03, int>(0); check<bar::type03, int>(0); std::cout << std::endl;
  72. 	std::cout << "type04   "; bar::check<bar::type04, int>(0); check<bar::type04, int>(0); std::cout << std::endl;
  73. 	std::cout << "type05   "; bar::check<bar::type05, int>(0); check<bar::type05, int>(0); std::cout << std::endl;
  74. 	std::cout << "type06   "; bar::check<bar::type06, int>(0); check<bar::type06, int>(0); std::cout << std::endl;
  75. 	std::cout << "type07   "; bar::check<bar::type07, int>(0); check<bar::type07, int>(0); std::cout << std::endl;
  76. 	std::cout << "type08   "; bar::check<bar::type08, int>(0); check<bar::type08, int>(0); std::cout << std::endl;
  77. 	std::cout << "type09   "; bar::check<bar::type09, int>(0); check<bar::type09, int>(0); std::cout << std::endl;
  78. 	std::cout << "type10   "; bar::check<bar::type10, int>(0); check<bar::type10, int>(0); std::cout << std::endl;
  79. 	std::cout << std::endl;
  80.  
  81. 	return 0;
  82. }
Success #stdin #stdout 0s 15240KB
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stdin
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Standard input is empty
stdout
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-- compiled with clang --
-- compiled with GCC --

         inside of bar:              outside of bar:             
type01   > can be instantiated       > can NOT be instantiated   
type02   > can be instantiated       > can be instantiated       
type03   > can be instantiated       > can be instantiated       
type04   > can be instantiated       > can NOT be instantiated   
type05   > can be instantiated       > can be instantiated       
type06   > can NOT be instantiated   > can NOT be instantiated   
type07   > can be instantiated       > can be instantiated       
type08   > can NOT be instantiated   > can NOT be instantiated   
type09   > can NOT be instantiated   > can NOT be instantiated   
type10   > can be instantiated       > can be instantiated
https://ideone.com/cdB5lZ
language:
C++14 (clang 8.0)
created:
7 years ago
visibility:
secret

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