Simple factory pattern

• idiomFactory1.cc:

  /*
      Test a simple factory idiom.  Factory creates an object
      of a derived type of Base and delivers the object 
      to the caller upon demand. 
      
      \author Oliver Schoenborn
      \since Apr 2003
  */
  
  
  #include "Deriveds.hh"
  #include "DynObj.hh"
  using namespace NoPtr;
  
  /*
      A simple factory class.
  */
  class FactoryOne
  {
      DynObj<Base> owner;
      
      public:
          void create(const std::string& type) 
          {
              if (type=="derived1")
                  owner.acquire(new Derived1);
              else if (type=="derived2")
                  owner.acquire(new Derived2);
              else throw std::logic_error("Unknown type");
          }
          
          void getObj( DynObj<Base>& newOwned )
          { 
              std::cout << "FactoryOne: giving object" << std::endl;
              if (owner.isNull()) 
                  throw std::logic_error("No object created");
              Base* const tmp = owner.getPtr();
              newOwned.acquire( owner );
              assert(owner.isNull());
              assert(newOwned.getPtr() == tmp);
          }
  };
  
  /* Use factory to make object of given type, call method on it.
  */
  void make(FactoryOne& factory, const std::string& type)
  {
      factory.create(type);
      
      DynObj<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;
      }
  }
  
  /*
      Output (for g++ 3.2):
      
      Using FactoryOne
      Instantiating an 8Derived1# 1
      FactoryOne: giving object
      8Derived1::callVirtual()# 1
      Destroying an 8Derived1# 1
      Instantiating an 8Derived2# 2
      FactoryOne: giving object
      8Derived2::callVirtual()# 2
      Destroying an 8Derived2# 2
  */
  

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