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  1. #include <iostream>
  2.  
  3. template <typename...>
  4. struct wrapper
  5. {
  6.   static void foo() {
  7.     std::cout << "generic" << std::endl;
  8.   }
  9. };
  10.  
  11. template<typename T>
  12. struct wrapper<T>
  13. {
  14.   static void foo() {
  15.     std::cout << "one argument" << std::endl;
  16.   }
  17. };
  18.  
  19. // just an illustration
  20. template <typename T>              // <--------------------------------------------------+
  21. struct wrapper <int, double, T>    // <--- to instantiate, use this list of arguments    |
  22. {                                  //          not this one -----------------------------+
  23.                                    //          that is, say `wrapper<int, double, sometype>`
  24.   static void foo() {
  25.     std::cout << "three arguments (int, double, something)" << std::endl;
  26.   }
  27. };
  28.  
  29. template <template<typename ...> class T,   // <-----------------------------------------+
  30.          typename K>               //                                                    |
  31. struct wrapper<T<K>>               // <--- to instantiate, use this list of arguments    |
  32. {                                  //         not this one ------------------------------+
  33.                                    //         that is, say `wrapper<sometemplate<sometype>>`
  34.   static void foo() {
  35.         std::cout << "the template thingy" << std::endl;
  36.   }
  37. };
  38.  
  39. template <typename> class X {};
  40.  
  41. int main ()
  42. {
  43.   wrapper<int, int>::foo();
  44.   wrapper<int>::foo();
  45.   wrapper<int, double, X<int>>::foo();
  46.   wrapper<X<int>>::foo();
  47. }
  48.  
Success #stdin #stdout 0s 3340KB
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Standard input is empty
stdout
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generic
one argument
three arguments (int, double, something)
the template thingy
https://ideone.com/RwWOnh
language:
C++14 (gcc 8.3)
created:
10 years ago
visibility:
secret

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