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  1. #include <type_traits>
  2. #include <iostream>
  3.  
  4. struct _test_print {
  5.     template<class T> static auto test(T* p) -> decltype(p->print(), std::true_type());
  6.     template<class>        static auto test(...) -> std::false_type;
  7. };
  8. template<class T> struct has_print : public decltype(_test_print::test<T>(0)) {};
  9.  
  10.  
  11. template<typename T>
  12. auto print(T t) -> typename std::enable_if<has_print<T>::value, decltype(t.print())>::type {
  13.     return t.print();
  14. }
  15.  
  16. template<typename T>
  17. auto print(T t) -> typename std::enable_if<!has_print<T>::value, T>::type {
  18.     return t;
  19. }
  20.  
  21.  
  22. struct MyClass {
  23.     std::string print() {
  24.         return "I was printed using my custom print()!";
  25.     }
  26. };
  27.  
  28. int main() {
  29.     MyClass myobj;
  30.     std::cout << print(42) << std::endl;
  31.     std::cout << print(myobj) << std::endl;
  32. }
Success #stdin #stdout 0s 3028KB
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stdin
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Standard input is empty
stdout
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42
I was printed using my custom print()!
https://ideone.com/WMhh7k
language:
C++14 (gcc 8.3)
created:
12 years ago
visibility:
secret

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