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  1. #include <iostream>
  2. #include <limits>
  3. #include <type_traits>
  4.  
  5. using namespace std;
  6.  
  7. struct vec
  8.   { double x;double y;double z; };
  9.  
  10. namespace details
  11. {
  12.  template <typename T>
  13.  constexpr double X(const T& param) { return param.x; }
  14.  
  15.  template <typename T>
  16.  constexpr double Y(const T& param) { return param.y; }
  17.  
  18.  template <typename T>
  19.  constexpr double Z(const T& param) { return param.z; }
  20. }
  21.  
  22. template <typename T, typename = void>
  23. constexpr double (*my_temp[])(const vec&) = { &details::X<T>, &details::Y<T> };
  24.  
  25. template <typename T>
  26. constexpr double (*my_temp<T, 
  27.                   enable_if_t<is_floating_point
  28.                   < decltype(details::X(T()))>::value>>[])(const vec&) = 
  29.                   { &details::X<T>, &details::Y<T>, &details::Z<T> };
  30.  
  31.  
  32. int main() {
  33.   vec foo = { 1.0, 2.0, 3.0 };
  34.  
  35.   for(const auto i : my_temp<decltype(foo)>) {
  36.     cout << (*i)(foo) << endl;
  37.   }
  38. }
Success #stdin #stdout 0.01s 5320KB
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https://ideone.com/51shW0
language:
C++14 (gcc 8.3)
created:
12 hours ago
visibility:
public

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