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  1. #include <algorithm>
  2. #include <cassert>
  3. #include <memory>
  4. #include <vector>
  5.  
  6. struct Getter {
  7.   virtual int get() const = 0;
  8. };
  9.  
  10. struct Changer {
  11.   virtual void change(int v) = 0;
  12. };
  13.  
  14. struct DataStorage;
  15.  
  16. typedef std::vector<std::unique_ptr<DataStorage> > MList;
  17.  
  18. struct Registrar {
  19.   Registrar(MList &mlist) : mlist(mlist) { }
  20.   void add(std::unique_ptr<DataStorage>);
  21.  
  22.   private:
  23.     MList &mlist;
  24. };
  25.  
  26. void Registrar::add(std::unique_ptr<DataStorage> item)
  27. {
  28.   mlist.push_back(std::move(item));
  29. }
  30.  
  31. // Plugins can create new instances of this class as needed
  32. struct DataStorage : Getter, Changer {
  33.   public:
  34.     DataStorage(int v)
  35.       : val(v)
  36.     {
  37.     }
  38.  
  39.     virtual int get() const { return val; }
  40.     virtual void change(int v) { val = v; }
  41.  
  42.   protected:
  43.     int val;
  44. };
  45.  
  46. // List of data storage objects templated on which interface
  47. // we want.
  48. template <typename Base>
  49. struct DataStorageList {
  50.   struct ItemAccessor {
  51.     ItemAccessor(MList &mlist)
  52.       : iter(mlist.begin()), end(mlist.end())
  53.     {
  54.     }
  55.  
  56.     // Returns a null pointer if there are no more items
  57.     Base *nextPtr()
  58.     {
  59.       if (iter==end) return 0;
  60.       return (*iter++).get();
  61.     }
  62.  
  63.     private:
  64.       MList::iterator iter, end;
  65.   };
  66.  
  67.   DataStorageList(MList &mlist) : mlist(mlist) { }
  68.  
  69.   ItemAccessor itemAccessor() const
  70.   {
  71.     return ItemAccessor(mlist);
  72.   }
  73.  
  74.   private:
  75.     MList &mlist;
  76. };
  77.  
  78. struct Plugin {
  79.   void initialize(Registrar &registrar)
  80.   {
  81.     // Use registrar to register new data storage objects if needed
  82.     registrar.add(std::unique_ptr<DataStorage>(new DataStorage(1)));
  83.   }
  84.  
  85.   void run(DataStorageList<Getter> getter_list)
  86.   {
  87.     // Use getter_list if you need access to the data storage objects
  88.     // but only as getters.
  89.     DataStorageList<Getter>::ItemAccessor
  90.       item_accessor = getter_list.itemAccessor();
  91.     while (Getter *getter_ptr = item_accessor.nextPtr()) {
  92.       // Do something with the getter_ptr
  93.     }
  94.   }
  95. };
  96.  
  97. int main(int,char**)
  98. {
  99.   MList mlist;
  100.   Registrar registrar(mlist);
  101.   Plugin plugin;
  102.   plugin.initialize(registrar);
  103.   DataStorageList<Getter> getter_list(mlist);
  104.   plugin.run(getter_list);
  105. }
  106.  
Success #stdin #stdout 0s 3024KB
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https://ideone.com/2VuHb9
language:
C++14 (gcc 8.3)
created:
12 years ago
visibility:
public

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