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  1. #include <unordered_map>
  2. #include <string>
  3. #include <iostream>
  4.  
  5. class Base
  6. {
  7. public:
  8.     typedef std::unordered_map<std::string, void*> registry_map;
  9.  
  10.     virtual ~Base() = default;
  11.  
  12.     static registry_map & registry()
  13.     {
  14.         static registry_map impl;
  15. 	    return impl;
  16.     }
  17.     template<typename ...T>
  18.     static Base * instantiate(std::string const & name, T&&...args)
  19.     {
  20. 	    auto it = registry().find(name);
  21. 	    if ( it == registry().end()) return 0;
  22. 	    typedef Base* (*create_type)(T...);
  23. 	    auto create_fun = reinterpret_cast<create_type>(it->second);
  24. 	    return create_fun(args...);
  25.     }
  26.     virtual void f() = 0;
  27. };
  28.  
  29. struct Registrar
  30. {
  31. 	template<typename F>
  32. 	Registrar(std::string name, F func)
  33. 	{
  34. 		Base::registry()[name] = reinterpret_cast<void*>(func);
  35. 	}
  36. };
  37.  
  38. class DerivedExample : public Base
  39. {
  40.     static Registrar registrar;
  41. public:
  42.     static Base * create() { return new DerivedExample; }
  43.     virtual void f() override { std::cout << "DerivedExample" << std::endl; }
  44. };
  45.  
  46. Registrar DerivedExample::registrar("DerivedExample", DerivedExample::create);
  47.  
  48. class AnotherExample : public Base
  49. {
  50.     static Registrar registrar;
  51.     int a;
  52.     const char *b;
  53. public:
  54.     AnotherExample(int a, const char *b) : a(a), b(b) {}
  55.     static Base * create(int a, const char *b) { return new AnotherExample(a,b); }
  56.     virtual void f() override { std::cout << "AnotherExample. a = " << a << ", b = " << b << std::endl; }
  57. };
  58.  
  59. Registrar AnotherExample::registrar("AnotherExample", AnotherExample::create);
  60.  
  61. int main()
  62. {
  63. 	Base * p = Base::instantiate("DerivedExample");
  64. 	Base * q = Base::instantiate("AnotherExample", 10, "Mahfuza");
  65. 	p->f();
  66. 	q->f();
  67.  
  68.     delete p;
  69.     delete q;
  70. }
  71.  
Success #stdin #stdout 0s 3432KB
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stdin
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Standard input is empty
stdout
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DerivedExample
AnotherExample. a = 10, b = Mahfuza
https://ideone.com/LUWiao
language:
C++14 (gcc 8.3)
created:
11 years ago
visibility:
public

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