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  1. #include <cassert>
  2.  
  3. template<typename T1, typename T2>
  4.   struct is_same
  5. {
  6.   static const bool value = false;
  7. };
  8.  
  9. template<typename T>
  10.   struct is_same<T,T>
  11. {
  12.   static const bool value = true;
  13. };
  14.  
  15. template<typename F, typename Arg1>
  16.   struct parameter_type
  17. {
  18.   // what goes here?
  19. };
  20.  
  21. struct takes_int
  22. {
  23.   void operator()(int);
  24. };
  25.  
  26. struct takes_float_ref
  27. {
  28.   char operator()(float &);
  29. };
  30.  
  31. struct takes_float_cref
  32. {
  33.   int operator()(const float &);
  34. };
  35.  
  36. struct bar {};
  37.  
  38. struct something_convertible_to_bar
  39. {
  40.   operator bar ();
  41. };
  42.  
  43. struct takes_bar
  44. {
  45.   bar operator()(bar);
  46. };
  47.  
  48. struct takes_value
  49. {
  50.   template<typename T> void operator()(T);
  51. };
  52.  
  53. struct has_overloads
  54. {
  55.   bar operator()(int &);
  56.  
  57.   void operator()(const int &);
  58. };
  59.  
  60. int main()
  61. {
  62.   // int
  63.   assert((is_same<
  64.            parameter_type<takes_int, unsigned int>::type,
  65.            int
  66.          >::value));
  67.  
  68.   // float &
  69.   assert((is_same<
  70.            parameter_type<takes_float_ref, float>::type,
  71.            float &
  72.          >::value));
  73.  
  74.   // const float &
  75.   assert((is_same<
  76.            parameter_type<takes_float_cref, int>::type,
  77.            const float &
  78.          >::value));
  79.  
  80.   // bar
  81.   assert((is_same<
  82.            parameter_type<takes_bar, something_convertible_to_bar>::type,
  83.            bar
  84.          >::value));
  85.  
  86.   // int
  87.   assert((is_same<
  88.            parameter_type<takes_value, int &>::type,
  89.            int
  90.          >::value));
  91.  
  92.   // const int &
  93.   assert((is_same<
  94.            parameter_type<has_overloads, const int &>::type,
  95.            const int &
  96.          >::value));
  97.  
  98.   return 0;
  99. }
  100.  
  101.  
Compilation error #stdin compilation error #stdout 0s 0KB
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stdin
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Standard input is empty
compilation info 
prog.cpp: In function ‘int main()’:
prog.cpp:63: error: ‘type’ is not a member of ‘parameter_type<takes_int, unsigned int>’
prog.cpp:63: error: ‘type’ is not a member of ‘parameter_type<takes_int, unsigned int>’
prog.cpp:63: error: template argument 1 is invalid
prog.cpp:69: error: ‘type’ is not a member of ‘parameter_type<takes_float_ref, float>’
prog.cpp:69: error: ‘type’ is not a member of ‘parameter_type<takes_float_ref, float>’
prog.cpp:69: error: template argument 1 is invalid
prog.cpp:75: error: ‘type’ is not a member of ‘parameter_type<takes_float_cref, int>’
prog.cpp:75: error: ‘type’ is not a member of ‘parameter_type<takes_float_cref, int>’
prog.cpp:75: error: template argument 1 is invalid
prog.cpp:81: error: ‘type’ is not a member of ‘parameter_type<takes_bar, something_convertible_to_bar>’
prog.cpp:81: error: ‘type’ is not a member of ‘parameter_type<takes_bar, something_convertible_to_bar>’
prog.cpp:81: error: template argument 1 is invalid
prog.cpp:87: error: ‘type’ is not a member of ‘parameter_type<takes_value, int&>’
prog.cpp:87: error: ‘type’ is not a member of ‘parameter_type<takes_value, int&>’
prog.cpp:87: error: template argument 1 is invalid
prog.cpp:93: error: ‘type’ is not a member of ‘parameter_type<has_overloads, const int&>’
prog.cpp:93: error: ‘type’ is not a member of ‘parameter_type<has_overloads, const int&>’
prog.cpp:93: error: template argument 1 is invalid
stdout
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Standard output is empty
https://ideone.com/ouUHN
language:
C++ (gcc 8.3)
created:
12 years ago
visibility:
public

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