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  1. #include <type_traits> 
  2. #include <iostream>
  3.  
  4. //classes
  5. struct A { virtual ~A(){} virtual void print(){std::cout << "A\n";}};
  6. struct B : A { virtual void print(){std::cout << "B\n";}};
  7. struct C : A { virtual void print(){std::cout << "C\n";}};
  8. struct D : A { virtual void print(){std::cout << "D\n";}};
  9.  
  10. //polymorphic local forwarder
  11. template<class Type, class FuncType>
  12. auto poly_local(FuncType func) -> decltype(func(std::declval<Type&>()))
  13. {
  14.     Type local;
  15.     return func(local);
  16. }
  17.  
  18. //test function
  19. char dowork(A& a) {
  20.     a.print();
  21.     return '8';
  22. }
  23. //test functionoid with parameters
  24. struct dowork2 {
  25.     int parameter;
  26.     explicit dowork2(int p) :parameter(p) {}
  27.     int operator()(A& a) const{
  28.         a.print();
  29.         std::cout << parameter << '\n';
  30.         return parameter;
  31.     }
  32. };
  33.  
  34. //demo
  35. int main() {
  36.     int some_var = 2;
  37.  
  38.     switch (some_var) {
  39.     case 1: poly_local<A>(dowork); break;
  40.     case 2: poly_local<B>(dowork); break;
  41.     default: poly_local<C>(dowork); break;
  42.     }
  43.  
  44.     switch (some_var) {
  45.     case 1: poly_local<B>(dowork2(3)); break;
  46.     case 2: poly_local<C>(dowork2(2)); break;
  47.     default: poly_local<A>(dowork2(1)); break;
  48.     }
  49.     return 0;
  50. }
Success #stdin #stdout 0s 2928KB
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B
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https://ideone.com/8OFNK
language:
C++14 (gcc 8.3)
created:
12 years ago
visibility:
secret

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