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Simple factory pattern

• testIdiomFactory1.cc:

  /*
      \file
      Test a simple factory idiom.  Factory creates an object
      of a derived type of Base and delivers the object 
      to the caller upon demand. 
  */
  
  #include "Deriveds.hh"
  #include "OwnedPtr.hh"
  using namespace MangoPtr;
  
  /*
      A simple factory class.
  */
  class FactoryOne
  {
      Owned<Base*> owner;
      
      public:
          void create(const std::string& type) 
          {
              if (type=="derived1")
                  owner.takeOwnership(new Derived1);
              else if (type=="derived2")
                  owner.takeOwnership(new Derived2);
              else throw std::logic_error("Unknown type");
          }
          
          void getObj( Owned<Base*>& newOwned )
          { 
              std::cout << "FactoryOne: giving object" << std::endl;
              if (owner.isNull()) 
                  throw std::logic_error("No object created");
              newOwned.takeOwnership( owner.giveOwnership() );
          }
  };
  
  /* Use factory to make object of given type, call method on it.
  */
  void make(FactoryOne& factory, const std::string& type)
  {
      factory.create(type);
      
      Owned<Base*> mango;
      factory.getObj(mango);
      assert(mango.isNotNull());
      
      mango()->callVirtual();    
  }
  
  int main()
  {
      try
      {
          std::cout << "Using FactoryOne" << std::endl;
          FactoryOne factory;
          make(factory, "derived1");
          make(factory, "derived2");
      }
      catch (const std::exception& e)
      {
          std::cout << e.what() << std::endl;
      }
  }
  
  

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