G4CreatorFactoryT.hh

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//
// Generic identifier-creator based factory. Based on 
// factory presented in "Modern C++ Design, Andrei Alexandrescu"
//
// Jane Tinslay, September 2006
//
#ifndef G4CREATORFACTORYT_HH
#define G4CREATORFACTORYT_HH

#include "globals.hh"
#include <map>

template <typename T, typename Identifier, typename Creator>
class G4CreatorFactoryT {

public:

  // Constructor
  G4CreatorFactoryT();

  // Destructor
  virtual ~G4CreatorFactoryT();

  // Register identifier<->creator pairs
  G4bool Register(const Identifier& id, Creator creator);

  // Create product with given identifier
  T* Create(const Identifier& id) const; 

private:

  typedef std::map<Identifier, Creator> Map;

  // Data member
  Map fMap;

};

template <typename T, typename Identifier, typename Creator>
G4CreatorFactoryT<T, Identifier, Creator>::G4CreatorFactoryT() {}

template <typename T, typename Identifier, typename Creator>
G4CreatorFactoryT<T, Identifier, Creator>::~G4CreatorFactoryT() {}

template <typename T, typename Identifier, typename Creator>
G4bool
G4CreatorFactoryT<T, Identifier, Creator>::Register(const Identifier& id, 
                                                    Creator creator)
{
  if (fMap.find(id) != fMap.end()) {
    G4ExceptionDescription ed;
    ed << "Creator with identifier "<<id<<" already exists."<<G4endl;
    G4Exception
      ("G4CreatorFactoryT::Register(const Identifier& id, Creator creator)",
       "greps0102", JustWarning, ed,
       "Creator exists");
    return false;
  }

  // Insert identifier<->creator pair into map
  std::pair<Identifier, Creator> myPair(id, creator);
  return fMap.insert(myPair).second;
}

template <typename T, typename Identifier, typename Creator>
T* 
G4CreatorFactoryT<T, Identifier, Creator>::Create(const Identifier& id) const
{
  typename Map::const_iterator iter = fMap.find(id);
  
  if (iter == fMap.end()) {
    G4ExceptionDescription ed;
    ed << "Identifier "<<id<<" does not exist."<<G4endl;
    G4Exception("G4CreatorFactoryT::Create(const Identifier& id)",
                "greps0103", JustWarning, ed,
                "Non-existent identifier");
    return 0;
  }
  
  return iter->second();
}

#endif