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  1. #include <memory>
  2.  
  3. template<typename> class FactoryImpl;
  4.  
  5. template<> class FactoryImpl<void> {
  6.   struct secret { };
  7.   friend class Base;
  8. };
  9.  
  10. template<typename T>
  11. class FactoryImpl : T {
  12.   public:
  13.     template<typename... Args>
  14.     static std::unique_ptr<class Base> create (Args&&... args) {
  15.       return std::unique_ptr<class Base> (new FactoryImpl (std::forward<Args> (args) ...));
  16.     }
  17.  
  18.   private:
  19.     template<typename... Args>
  20.     FactoryImpl (Args&&... args)
  21.       : T (std::forward<Args> (args) ... )
  22.     { }
  23.  
  24.     virtual void _not_allowed (FactoryImpl<void>::secret) { };
  25. };
  26.  
  27. class Base {
  28.   public:
  29.     virtual ~Base () { }
  30.  
  31.   private:
  32.     virtual void _not_allowed (FactoryImpl<void>::secret) = 0;
  33. };
  34.  
  35. template<typename T, typename... Args>
  36. std::unique_ptr<Base> factory (Args&&... args) {
  37.   return FactoryImpl<T>::create (std::forward<Args> (args) ...);
  38. }
  39.  
  40.  
  41. struct Derived : Base {
  42.   Derived ()      { }
  43.   Derived (int i) { }
  44. };
  45.  
  46.  
  47. int
  48. main (int argc, char *argv[])
  49. {
  50.   factory<Derived> ();
  51.   factory<Derived> (123);
  52.  
  53.   // Derived d; // <- ERROR
  54. }
  55.  
Success #stdin #stdout 0s 3424KB
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https://ideone.com/GCIrAF
language:
C++14 (gcc 8.3)
created:
11 years ago
visibility:
public

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