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  1. // ----------------------------------------------------------
  2. // qmetatype.h simplification -------------------------------
  3. // ----------------------------------------------------------
  4.  
  5. template<typename T>
  6. struct metatype
  7. {
  8.  enum { defined = 0 };
  9. };
  10.  
  11. template<typename T>
  12. struct metatype2
  13. {
  14.  enum { defined = metatype<T>::defined };
  15.  static inline int id() { return metatype<T>::id(); }
  16. };
  17.  
  18. template <typename T>
  19. inline int metatypeId(
  20.     T * /* dummy */ = 0
  21. )
  22. {
  23.     return metatype2<T>::id();
  24. }
  25.  
  26. #define register_meta_type( _type_ )  \
  27.  template<>                           \
  28.  struct metatype< _type_ >            \
  29.  {                                    \
  30.   enum { defined = 1 };               \
  31.   static int id()                     \
  32.   {                                   \
  33.    /* Run-time registration in Qt */  \
  34.    return __COUNTER__;                \
  35.   };                                  \
  36.  };
  37.  
  38.  
  39.  
  40. // ----------------------------------------------------------
  41. // ----------------------------------------------------------
  42. // ----------------------------------------------------------
  43.  
  44. class TestA {};
  45. register_meta_type(TestA)
  46.  
  47. class TestB {};
  48.  
  49. class TestC {};
  50. register_meta_type(TestC)
  51.  
  52. class TestD {};
  53.  
  54.  
  55. #include <type_traits>
  56.  
  57. struct _test_is_declared_metatype
  58. {
  59.  /*
  60.    metatypeId<T>() is always a valid expression. So this overload is
  61.    always taken
  62.  */
  63.     template<class T>
  64.     static auto test(T* t) -> decltype(metatypeId<T>(), std::true_type());
  65.  
  66.     static std::false_type test(...);
  67. };
  68.  
  69. template<class T>
  70. struct is_declared_metatype : decltype(_test_is_declared_metatype::test<T>(0))
  71. {
  72. };
  73.  
  74. #include <iostream>
  75. #define PRINT_DEF( _type_ )  std::cout << #_type_ << " registered ? " << is_declared_metatype< _type_ >::value << "\n";
  76. int main()
  77. {
  78.  std::cout << std::boolalpha;
  79.  PRINT_DEF(TestA);
  80.  PRINT_DEF(TestB);
  81.  PRINT_DEF(TestC);
  82.  PRINT_DEF(TestD);
  83. }
Success #stdin #stdout 0s 2896KB
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Standard input is empty
stdout
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TestA registered ? true
TestB registered ? true
TestC registered ? true
TestD registered ? true
https://ideone.com/jcv6a2
language:
C++14 (gcc 8.3)
created:
11 years ago
visibility:
public

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