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  1. #include <map>
  2. #include <iostream>
  3. using namespace std;
  4.  
  5. class A
  6.   {
  7.    public:
  8.    typedef A *creator();
  9.    typedef map<int,creator*> creatormap;
  10.    static creatormap &getmap()
  11.      {
  12.       static creatormap amap;	
  13.       return amap;
  14.      }
  15.    template<class T> static void reg(int value)
  16.      {
  17.       getmap()[value]=[] () -> A* { return new T(); };
  18.      }
  19.    static A *make(int value)
  20.      {
  21.       creator *fun=getmap()[value];
  22.       return (fun?fun():0);
  23.      }
  24.   };
  25.  
  26. class B:public A
  27.   {
  28.    public:
  29.    B() { cout<<"B"<<endl; }
  30.   };
  31.  
  32. class C:public A
  33.   {
  34.    public:
  35.    C() { cout<<"C"<<endl; }
  36.   };
  37.  
  38. class D:public C
  39.   {
  40.    public:
  41.    D() { cout<<"D"<<endl; }
  42.   };
  43.  
  44. void reg()
  45.   {
  46.    A::reg<B>(1);
  47.    A::reg<C>(2);
  48.    A::reg<D>(3);
  49.   }
  50.  
  51. int main()
  52.   {
  53.    reg();
  54.    A *b=A::make(1); 
  55.    A *c=A::make(2);
  56.    A *d=A::make(3);
  57.    A *a=A::make(0);
  58.    if(!a) cout<<"is NULL and it is OK"<<endl;
  59.    delete b;
  60.    delete c;
  61.    delete d;
  62.    return 0;
  63.   }
Success #stdin #stdout 0s 3476KB
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stdin
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Standard input is empty
stdout
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B
C
C
D
is NULL and it is OK
https://ideone.com/F5aFOS
language:
C++14 (gcc 8.3)
created:
9 years ago
visibility:
secret

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