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  1. #include <iostream>
  2. using namespace std;
  3.  
  4. template <bool isConstexpr>
  5. struct f_impl;
  6.  
  7. template <>
  8. struct f_impl<false>
  9. {
  10. 	static int f(int a)
  11. 	{
  12. 		cout << "well, I'm not constexpr f()\n";
  13. 		return a;
  14. 	}
  15. };
  16.  
  17. constexpr int f_constexpr(int a)
  18. {
  19. 	return a;
  20. }
  21.  
  22. template <>
  23. struct f_impl<true>
  24. {
  25. 	static constexpr int f(int a)
  26. 	{
  27. 		return f_constexpr(a);
  28. 	}
  29. };
  30.  
  31.  
  32. #define f(a) f_impl<noexcept(f_constexpr(a))>::f(a)
  33.  
  34. int main(int argc, char* argv[]) {
  35. 	constexpr int a = f(7);
  36.     cout << "constexpr was called..." << endl; 
  37. 	int c = f(argc);
  38.     cout << "non constexpr was called, I guess..." << endl; 
  39. 	cout << a << endl;
  40. 	cout << c << endl;
  41.  
  42. }
Success #stdin #stdout 0s 3460KB
comments (?)
stdin 
Standard input is empty
stdout 
constexpr was called...
well, I'm not constexpr f()
non constexpr was called, I guess...
7
1
https://ideone.com/M45rJx
language:
C++14 (gcc 8.3)
created:
10 years ago
visibility:
secret

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