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  1. //User types
  2. struct field_t{};
  3. struct other_t{};
  4. struct StructA{field_t field;};
  5. struct StructB{other_t other;};
  6. struct StructC:public StructA{};
  7. struct StructD:public StructB{};
  8. struct StructT{other_t field;field_t other;};
  9. //Implementation detail
  10. template<typename T,typename FIELD_T>
  11. struct type_has_field{
  12.   struct Fallback {FIELD_T field;};
  13.   struct Derived:T,Fallback{};
  14.   template<typename C, C> struct ChT;
  15.   template<typename C> static char (&f(ChT<FIELD_T Fallback::*, &C::field>*))[1];
  16.   template<typename C> static char (&f(...))[2];
  17.  
  18.   static bool const value = sizeof(f<Derived>(0)) == 2;
  19. };
  20. //Experiment
  21. void UnitTest(){
  22.   static_assert(
  23.     true==type_has_field<StructA,field_t>::value,
  24.     "field_t StructA::field - should exist"
  25.   );
  26.   static_assert(
  27.     false==type_has_field<StructB,field_t>::value,
  28.     "field_t StructB::field - should not exist"
  29.   );
  30.   static_assert(
  31.     true==type_has_field<StructC,field_t>::value,
  32.     "field_t StructC::field - should exist"
  33.   );  
  34.   static_assert(
  35.     false==type_has_field<StructD,field_t>::value,
  36.     "field_t StructD::field - should not exist"
  37.   );
  38.   static_assert(
  39.     false==type_has_field<StructT,field_t>::value,
  40.     "field_t StructT::field - should not exist"
  41.   );
  42.   static_assert(
  43.     true==type_has_field<StructT,other_t>::value,
  44.     "other_t StructT::field - should exist"
  45.   );
  46. }
  47. int main(){return 0;}
Compilation error #stdin compilation error #stdout 0s 0KB
comments (?)
stdin
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Standard input is empty
compilation info 
prog.cpp: In function ‘void UnitTest()’:
prog.cpp:38:3: error: static assertion failed: field_t StructT::field - should not exist
   static_assert(
   ^
stdout
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Standard output is empty
https://ideone.com/1uwtY6
language:
C++14 (gcc 8.3)
created:
10 years ago
visibility:
secret

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