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  1. #include <iostream>
  2. #include <map>
  3. #include <memory>
  4. #include <stdexcept>
  5.  
  6. class Base
  7. {
  8. public:
  9.     //...
  10.     virtual int getId() const = 0;
  11. };
  12.  
  13. class Derived1: public Base
  14. {
  15. public:
  16.     //...
  17.     int getId() const override { return 0; }
  18. };
  19.  
  20. class Derived2: public Base
  21. {
  22. public:
  23.     //...
  24.     int getId() const override { return 1; }
  25. };
  26.  
  27. //...
  28.  
  29. using createFunc = std::shared_ptr<Base>(*)();
  30.  
  31. static std::map<int, createFunc> myMap
  32. {
  33.     {0, []() -> std::shared_ptr<Base> { return std::make_shared<Derived1>(); }},
  34.     {1, []() -> std::shared_ptr<Base> { return std::make_shared<Derived2>(); }}
  35.     //...
  36. };
  37.  
  38. static std::shared_ptr<Base> createInstance(int id)
  39. {
  40.     auto iter = myMap.find(id);
  41.     if (iter == myMap.end())
  42.         throw std::out_of_range("Unknown id");
  43.     return iter->second();
  44. }
  45.  
  46. static int getId(Base* instance)
  47. {
  48.     return instance->getId();
  49. }
  50.  
  51. int main()
  52. {
  53. 	auto inst1 = createInstance(0);
  54. 	std::cout << getId(inst1.get()) << std::endl;
  55.  
  56. 	auto inst2 = createInstance(1);
  57. 	std::cout << getId(inst2.get()) << std::endl;
  58.  
  59. 	try
  60. 	{
  61. 		auto inst3 = createInstance(3);
  62. 		std::cout << getId(inst3.get()) << std::endl;
  63. 	}
  64. 	catch (const std::exception &e)
  65. 	{
  66. 		std::cout << e.what() << std::endl;
  67. 	}
  68.  
  69. 	return 0;
  70. }
Success #stdin #stdout 0s 4312KB
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Unknown id
https://ideone.com/GTCgsZ
language:
C++ (gcc 8.3)
created:
5 years ago
visibility:
public

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