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  1. #include <iostream>
  2. #include <memory>
  3. #include <tuple>
  4.  
  5. struct Base { };
  6. struct A : Base { A(int) {} ~A() { std::cout << "~A\n"; } };
  7. struct B : Base { B(int) {} ~B() { std::cout << "~B\n"; } };
  8. struct C : Base { C(int) {} ~C() { std::cout << "~C\n"; } };
  9.  
  10. template<int... Is>
  11. struct indices { typedef indices type; };
  12.  
  13. template<int N, int... Is>
  14. struct make_indices : make_indices<N - 1, N - 1, Is...> { };
  15.  
  16. template<int... Is>
  17. struct make_indices<0, Is...> : indices<Is...> { };
  18.  
  19. template<typename... Types>
  20. struct Factory
  21. {
  22.     typedef std::tuple<Types...> TypesTuple;
  23.  
  24.     std::shared_ptr<Base> operator()(int const index)
  25.     {
  26.         return produce(index);
  27.     }
  28.  
  29.     std::shared_ptr<Base> produce(int const index)
  30.     {
  31.         return produce_impl(make_indices<sizeof...(Types)>(), index);
  32.     }
  33.  
  34.     template<int I, int... Is>
  35.     std::shared_ptr<Base> produce_impl(indices<I, Is...>, int const index)
  36.     {
  37.         if (I == index) {
  38.             return std::make_shared<typename std::tuple_element<I, TypesTuple>::type>(42);
  39.         }
  40.  
  41.         return produce_impl(indices<Is...>(), index);
  42.     }
  43.  
  44.     std::shared_ptr<Base> produce_impl(indices<>, int const index)
  45.     {
  46. 		throw "Uh-oh!";
  47.     }
  48. };
  49.  
  50. int main()
  51. {
  52. 	Factory<A, B, C> fac;
  53. 	fac(0);
  54. 	fac(1);
  55. 	fac(2);
  56. 	fac(3); // cause exception.
  57. }
  58.  
Runtime error #stdin #stdout #stderr 0s 3476KB
comments ()
stdin
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Standard input is empty
stdout
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~A
~B
~C
stderr
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terminate called after throwing an instance of 'char const*'
https://ideone.com/Ipk8YM
language:
C++14 (gcc 8.3)
created:
11 years ago
visibility:
secret

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