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  1.     #include <iostream>
  2.     #include <functional>
  3.     #include <memory>
  4.     #include <unordered_map>
  5.  
  6.     template <typename BASE>
  7.     struct
  8.     Factory {
  9.         private: using
  10.         TCloneFn = std::function<std::shared_ptr<BASE>(BASE const * const)>;
  11.  
  12.         private:
  13.         static std::unordered_map<BASE const*,TCloneFn> cloneFnMap;
  14.  
  15.         public: template <typename DERIVED_TYPE, typename...TS>
  16.         static std::shared_ptr<BASE>
  17.         create(TS...args) {
  18.             BASE* obj = new DERIVED_TYPE(args...);
  19.             const std::shared_ptr<BASE> pNewObj =
  20.                 std::shared_ptr<BASE>(
  21.                     obj,
  22.                     [&](BASE* p){
  23.                         cloneFnMap.erase(p);
  24.                         delete p;
  25.                     }
  26.                 );
  27.  
  28.             cloneFnMap[obj] = [&](BASE const * const orig){
  29.                 std::shared_ptr<BASE> pClone = create<DERIVED_TYPE>(std::ref(static_cast<DERIVED_TYPE const &>(*orig)));
  30.                 return pClone;
  31.             };
  32.             return pNewObj;
  33.         }
  34.  
  35.         public: static std::shared_ptr<BASE>
  36.         clone(std::shared_ptr<BASE const> original) {
  37.             return cloneFnMap[original.get()](original.get());
  38.         }
  39.     };
  40.  
  41.     template <typename BASE> std::unordered_map<BASE const*,typename Factory<BASE>::TCloneFn> Factory<BASE>::cloneFnMap;
  42.  
  43.     class Base {
  44.         public: virtual ~Base() throw() {}
  45.         public: virtual void whoAmI() const {
  46.             std::cout << "I am Base instance " << this << "\n";
  47.         }
  48.     };
  49.  
  50.  
  51.     class Derived : public Base {
  52.         std::string name;
  53.         public: Derived(std::string name) : name(name) {}
  54.         public: Derived(const Derived&other) : name("copy of "+other.name) {
  55.         }
  56.         private: virtual void whoAmI() const {
  57.             std::cout << "I am Derived instance " << this << " " << name << "\n";
  58.         }
  59.     };
  60.  
  61.     int main() {
  62.         std::shared_ptr<Base> a = Factory<Base>::create<Derived>("Original");
  63.         a->whoAmI();
  64.         std::shared_ptr<Base> copy_of_a = Factory<Base>::clone(a);
  65.         copy_of_a->whoAmI();
  66.         std::shared_ptr<Base> copy_of_a_copy = Factory<Base>::clone(copy_of_a);
  67.         copy_of_a_copy->whoAmI();
  68.         return 0;
  69.     }
  70.  
  71.  
  72.  
  73.  
Success #stdin #stdout 0s 3280KB
comments (?)
stdin
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Standard input is empty
stdout
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I am Derived instance 0x94dd058 Original
I am Derived instance 0x94dd0b0 copy of Original
I am Derived instance 0x94dd130 copy of copy of Original
https://ideone.com/kIPFt2
language:
C++14 (gcc 8.3)
created:
9 years ago
visibility:
public

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