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  1. #include <boost/shared_ptr.hpp>
  2. #include <boost/ptr_container/ptr_map.hpp>
  3. #include <iostream>
  4. #include <ostream>
  5. #include <map>
  6.  
  7. using namespace std;
  8. using namespace boost;
  9. typedef int ID;
  10.  
  11. struct SomeClass
  12. {
  13.     SomeClass()
  14.     {
  15.         cout << "SomeClass::SomeClass()" << endl;
  16.     }
  17.     ~SomeClass()
  18.     {
  19.         cout << "SomeClass::~SomeClass()" << endl;
  20.     }
  21. };
  22.  
  23. struct IVisitor
  24. {
  25.     virtual void visit(int)=0;
  26.     virtual void visit(double)=0;
  27.     virtual void visit(SomeClass&)=0;
  28.     // ..
  29. };
  30.  
  31. struct ConcreteVisitor: IVisitor
  32. {
  33.     virtual void visit(int)
  34.     {
  35.         cout << "visiting int" << endl;
  36.     }
  37.     virtual void visit(double)
  38.     {
  39.         cout << "visiting double" << endl;
  40.     }
  41.     virtual void visit(SomeClass&)
  42.     {
  43.         cout << "visiting SomeClass" << endl;
  44.     }
  45.     // ..
  46. };
  47.  
  48. struct ITypeStorage
  49. {
  50.     virtual void apply_visitor(void *obj,IVisitor &visitor)=0;
  51. };
  52.  
  53. template<typename ObjectType> struct TypeStorage: ITypeStorage
  54. {
  55.     virtual void apply_visitor(void *obj,IVisitor &visitor)
  56.     {
  57.         visitor.visit( *(static_cast<ObjectType *>(obj)) );
  58.     }
  59. };
  60.  
  61. class ObjectManager
  62. {
  63.     map<ID,boost::shared_ptr<void> > objects;
  64.     ptr_map<ID,ITypeStorage> types;
  65. public:
  66.     template <class T>
  67.     void create_object(ID id)
  68.     {
  69.         objects[id].reset(new T());//shared_ptr will use right deleter
  70.         types.insert(id,new TypeStorage<T>());
  71.     }
  72.     void apply(ID id,IVisitor &visitor)
  73.     {
  74.         types.find(id)->second->apply_visitor(objects[id].get(),visitor);
  75.     }
  76. };
  77.  
  78. int main(int argc,char *argv[])
  79. {
  80.     ObjectManager manager;
  81.     ConcreteVisitor visitor;
  82.  
  83.     manager.create_object<int>(1);
  84.     manager.create_object<double>(2);
  85.     manager.create_object<SomeClass>(3);
  86.  
  87.     manager.apply(1,visitor);
  88.     manager.apply(2,visitor);
  89.     manager.apply(3,visitor);
  90.     return 0;
  91. }
  92.  
Success #stdin #stdout 0.01s 2824KB
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stdin
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Standard input is empty
stdout
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SomeClass::SomeClass()
visiting int
visiting double
visiting SomeClass
SomeClass::~SomeClass()
https://ideone.com/qhmLax
language:
C++ (gcc 8.3)
created:
13 years ago
visibility:
secret

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