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  1. #include <iostream>
  2.  
  3. void do_something_with(int N) { std::cout << "2 + 3 = " << N << std::endl; }
  4.  
  5. template <int N>
  6. using int_c = std::integral_constant<int, N>;
  7.  
  8. // Compile time
  9. template <int N> void f(int_c<N>) = delete;
  10. void f(int_c<5>N) { do_something_with(N); }
  11.  
  12. // Runtime
  13. void f(int N){
  14.     if (N != 5){
  15.         std::abort();
  16.     }
  17.     f(int_c<5>{});
  18. }
  19.  
  20. template <std::size_t N>
  21. constexpr int to_number(const int (&a)[N])
  22. {
  23.     int res = 0;
  24.     for (auto e : a) {
  25.         res *= 10;
  26.         res += e;
  27.     }
  28.     return res;
  29. }
  30.  
  31. template <char ... Ns>
  32. constexpr int_c<to_number({(Ns - '0')...})> operator ""_c ()
  33. {
  34.     return {};
  35. }
  36.  
  37. int main(){
  38. 	f(5_c); // ok
  39.     // f(6_c); // error: use of deleted function ‘void f(int_c<N>) [with int N = 6; int_c<N> = std::integral_constant<int, 6>]’
  40. 	f(5); // ok
  41. 	std::cout << "it will abort" << std::endl;
  42.     f(6); // abort at runtime
  43. 	std::cout << "never reach" << std::endl;
  44. }
Runtime error #stdin #stdout 0s 15240KB
comments (?)
stdin 
Standard input is empty
stdout 
2 + 3 = 5
2 + 3 = 5
it will abort
https://ideone.com/z3xNmo
language:
C++14 (gcc 8.3)
created:
8 years ago
visibility:
public

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