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  1. #include <iostream>
  2. #include <typeinfo>
  3.  
  4. using namespace std;
  5.  
  6. template<typename FalseType, typename TrueType, bool condition>
  7. struct ConditionalTypeSelector
  8. {
  9.     typedef void ResultType;
  10. };
  11.  
  12. template<typename FalseType, typename TrueType>
  13. struct ConditionalTypeSelector<FalseType,TrueType,false>
  14. {
  15.     typedef FalseType ResultType;
  16. };
  17.  
  18. template<typename FalseType, typename TrueType>
  19. struct ConditionalTypeSelector<FalseType,TrueType,true>
  20. {
  21.     typedef TrueType ResultType;
  22. };
  23.  
  24. struct A {
  25.     unsigned char member;
  26. };
  27.  
  28. struct B {
  29.     int member;
  30. };
  31.  
  32. struct C {
  33.     long long member;
  34. };
  35.  
  36. int main() {
  37.     cout << typeid
  38.                 ( ConditionalTypeSelector
  39.                       < A,B,(sizeof(A) > sizeof(B))
  40.                       >::ResultType
  41.                 ).name() << endl;
  42.     cout << typeid
  43.                 ( ConditionalTypeSelector
  44.                       < A,B,(sizeof(B) > sizeof(A))
  45.                       >::ResultType
  46.                 ).name() << endl;
  47.  
  48.     cout << typeid
  49.                 ( ConditionalTypeSelector
  50.                       < A,C,(sizeof(A) > sizeof(C))
  51.                       >::ResultType
  52.                 ).name() << endl;
  53.  
  54.     cout << typeid
  55.                 ( ConditionalTypeSelector
  56.                       < C,B,true>::ResultType
  57.                 ).name() << endl;
  58.  
  59.     cout << typeid
  60.                 ( ConditionalTypeSelector
  61.                       < C,A,false>::ResultType
  62.                 ).name() << endl;
  63.  
  64.     return 0;
  65. }
  66.  
Success #stdin #stdout 0s 3296KB
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https://ideone.com/xFVY9r
language:
C++ (gcc 8.3)
created:
10 years ago
visibility:
public

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