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  1. #include <iostream>
  2. #include <stdexcept>
  3.  
  4. template<typename Base, typename Class, typename... Classes>
  5. struct Factory
  6. {
  7. private:
  8.     // creator proc
  9.     template<typename T>
  10.     static constexpr typename std::enable_if<std::is_base_of<Base,T>::value,Base>::type*
  11.     create()
  12.     {
  13.         return new T();
  14.     }
  15.  
  16.     // creator table
  17.     static Base* (*pfns[])();
  18.  
  19. public:
  20.     // return instance if in-range
  21.     Base* get(std::size_t i)
  22.     {
  23.         if (i > sizeof...(Classes))
  24.             throw std::out_of_range("Invalid class index");
  25.         return pfns[i]();
  26.     }
  27.  
  28.     // return number of supported derivations
  29.     static constexpr std::size_t size()
  30.     {
  31.         return sizeof...(Classes)+1;
  32.     }
  33. };
  34.  
  35. // static creator table
  36. template<typename Base, typename Class, typename... Classes>
  37. Base* (*Factory<Base,Class,Classes...>::pfns[])() =
  38. {
  39.     Factory<Base, Class, Classes...>::template create<Class>,
  40.     Factory<Base, Class, Classes...>::template create<Classes>...
  41. };
  42. ////////////////////////////////////////////////////////////////////////////////
  43.  
  44.  
  45. class Base
  46. {
  47. public:
  48.     virtual ~Base()
  49.     {
  50.         std::cout << __PRETTY_FUNCTION__ << std::endl;
  51.     }
  52. };
  53.  
  54. class DeriveOne : public Base
  55. {
  56. public:
  57.     DeriveOne()
  58.     {
  59.         std::cout << __PRETTY_FUNCTION__ << std::endl;
  60.     }
  61. };
  62.  
  63. class DeriveTwo : public Base
  64. {
  65. public:
  66.     DeriveTwo()
  67.     {
  68.         std::cout << __PRETTY_FUNCTION__ << std::endl;
  69.     }
  70. };
  71.  
  72. class DeriveThree : public DeriveTwo
  73. {
  74. public:
  75.     DeriveThree()
  76.     {
  77.         std::cout << __PRETTY_FUNCTION__ << std::endl;
  78.     }
  79. };
  80. ////////////////////////////////////////////////////////////////////////////////
  81.  
  82.  
  83. int main(int argc, char *argv[])
  84. {
  85.     Factory<Base, DeriveOne, DeriveTwo, DeriveThree> f1;
  86.  
  87.     for (std::size_t i=0; i<f1.size(); ++i)
  88.     {
  89.         Base *p = f1.get(i);
  90.         delete p;
  91.     }
  92.  
  93.     return EXIT_SUCCESS;
  94. }
Success #stdin #stdout 0s 3432KB
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Standard input is empty
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DeriveOne::DeriveOne()
virtual Base::~Base()
DeriveTwo::DeriveTwo()
virtual Base::~Base()
DeriveTwo::DeriveTwo()
DeriveThree::DeriveThree()
virtual Base::~Base()
https://ideone.com/AWGtBb
language:
C++14 (gcc 8.3)
created:
12 years ago
visibility:
secret

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