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  1. #include <iostream>
  2. #include <unordered_map>
  3. #include <typeindex>
  4. #include <functional>
  5.  
  6. using namespace std;
  7.  
  8. struct Container {
  9.  
  10.     template <class I, class C>
  11.     void assoc() {
  12.         generators[typeid(I)] = []() -> C * { return new C; };
  13.     }
  14.  
  15.     template <class I>
  16.     I * get() {
  17.         auto g = generators[typeid(I)];
  18.         return g ? static_cast<I *>(g()) : 0;
  19.     }
  20.  
  21.     unordered_map<type_index, function<void *(void)>> generators;
  22. };
  23.  
  24. struct IVehicle {
  25.     virtual void sayHello() = 0;
  26. };
  27.  
  28. struct Car : IVehicle {
  29.     void sayHello() override { cout << "Hello, I am a Car!" << endl; }
  30. };
  31.  
  32. struct Bicycle : IVehicle {
  33.     void sayHello() override { cout << "Hello, I am a Bicycle!" << endl; }
  34. };
  35.  
  36. void test(Container & c) {
  37.  
  38.     auto v = c.get<IVehicle>();
  39.  
  40.     if (v) {
  41.         v->sayHello();
  42.     } else {
  43.         cout << "Couldn't find vehicle :(" << endl;
  44.     }
  45.  
  46. }
  47.  
  48. int main() {
  49.  
  50.     Container c;
  51.  
  52.     test(c);
  53.  
  54.     c.assoc<IVehicle, Car>();
  55.     test(c);
  56.  
  57.     c.assoc<IVehicle, Bicycle>();
  58.     test(c);
  59.  
  60. }
Success #stdin #stdout 0s 3476KB
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stdin
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Standard input is empty
stdout
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Couldn't find vehicle :(
Hello, I am a Car!
Hello, I am a Bicycle!
https://ideone.com/nyIrwY
language:
C++14 (gcc 8.3)
created:
10 years ago
visibility:
secret

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