objectfactory.h

/* Copyright (C) 2004-2010 OpenMBV Development Team
 *
 * This library is free software; you can redistribute it and/or 
 * modify it under the terms of the GNU Lesser General Public 
 * License as published by the Free Software Foundation; either 
 * version 2.1 of the License, or (at your option) any later version. 
 *  
 * This library is distributed in the hope that it will be useful, 
 * but WITHOUT ANY WARRANTY; without even the implied warranty of 
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU 
 * Lesser General Public License for more details. 
 *  
 * You should have received a copy of the GNU Lesser General Public 
 * License along with this library; if not, write to the Free Software 
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301 USA
 *
 * Contact: friedrich.at.gc@googlemail.com
 */
 
#ifndef _OPENMBV_OBJECTFACTORY_H_
#define _OPENMBV_OBJECTFACTORY_H_
 
#include <map>
#include <stdexcept>
#include <typeinfo>
#include <typeindex>
#include <mbxmlutilshelper/dom.h>
#include <xercesc/dom/DOMElement.hpp>
#include <openmbvcppinterface/object.h>
 
namespace OpenMBV {
 
class Object;
 
class ObjectFactory {
 
  public:
 
    template<class CreateType>
    static void registerXMLName(const MBXMLUtils::FQN &name) {
      registerXMLNamePrivate(name, &defaultCTor<CreateType>);
      registerTypePrivate<CreateType>(&copyCTor<CreateType>);
    }
 
    template<class ContainerType>
    static std::shared_ptr<ContainerType> create(const xercesc::DOMElement *element) {
      // just check if ContainerType is derived from Object if not throw a compile error
      static_assert(std::is_convertible<ContainerType*, Object*>::value,
        "In OpenMBV::ObjectFactory::create<ContainerType>(...) ContainerType must be derived from Object.");
      // return NULL if no input is supplied
      if(element==nullptr) return {};
      // loop over all all registered types corresponding to element->ValueStr()
      auto range=instance().registeredName.equal_range(MBXMLUtils::E(element)->getTagName());
      for(auto it=range.first; it!=range.second; it++) {
        // allocate a new object using the defaultCTor function pointer
        std::shared_ptr<Object> ele=it->second();
        // try to cast ele up to ContainerType
        std::shared_ptr<ContainerType> ret=std::dynamic_pointer_cast<ContainerType>(ele);
        // if possible, return it
        if(ret)
          return ret;
      }
      // no matching element found: throw error
      throw std::runtime_error("No class named "+MBXMLUtils::X()%element->getTagName()+" found which is of type "+
                               typeid(ContainerType).name()+".");
    }
 
    template<class CreateType>
    static std::shared_ptr<CreateType> create() {
      return std::shared_ptr<CreateType>(new CreateType, &deleter<CreateType>);
    }
 
    template<class ContainerType>
    static std::shared_ptr<ContainerType> create(const std::shared_ptr<ContainerType> &t) {
      // return NULL if no input is supplied
      if(t==nullptr) return {};
      // find item
      auto &tRef=*t;
      auto it=instance().registeredType.find(std::type_index(typeid(tRef)));
      // not found?
      if(it==instance().registeredType.end())
        throw std::runtime_error(std::string("No class type ")+typeid(tRef).name()+" found in ObjectFactory.");
      // allocate a new object using the copyCTor function pointer
      return std::static_pointer_cast<ContainerType>(it->second(t));
    }
 
    static void addErrorMsg(const std::string &msg);
    static std::string getAndClearErrorMsg();
 
  private:
 
    // a pointer to a function allocating an object
    using DefaultCTor = std::shared_ptr<Object> (*)();
    using CopyCTor = std::shared_ptr<Object> (*)(const std::shared_ptr<Object>&);
 
    // convinence typedefs
    using MapName = std::multimap<MBXMLUtils::FQN, DefaultCTor>;
    using MapNameIt = typename MapName::iterator;
    using MapType = std::map<std::type_index, CopyCTor>;
    using MapTypeIt = typename MapType::iterator;
 
    // private ctor
    ObjectFactory() = default;
 
    static void registerXMLNamePrivate(const MBXMLUtils::FQN &name, DefaultCTor alloc);
 
    template<class CreateType>
    static void registerTypePrivate(CopyCTor alloc) {
      instance().registeredType.emplace(std::type_index(typeid(CreateType)), alloc);
    }
 
    // create an singleton instance of the object factory.
    // only declaration here and defition and explicit instantation for all Object in objectfactory.cc (required for Windows)
    static ObjectFactory& instance();
 
    // a multimap of all registered types
    MapName registeredName;
    MapType registeredType;
 
    // a wrapper to allocate an object of type CreateType by the default ctor: used by create(xercesc::DOMElement *)
    template<class CreateType>
    static std::shared_ptr<Object> defaultCTor() {
      return std::shared_ptr<CreateType>(new CreateType, &deleter<CreateType>);
    }
 
    // a wrapper to allocate an object of type CreateType by the copy ctor: used by create(const std::shared_ptr<Object>&)
    template<class CreateType>
    static std::shared_ptr<Object> copyCTor(const std::shared_ptr<Object> &t) {
      auto tCast=std::static_pointer_cast<CreateType>(t);
      return std::shared_ptr<CreateType>(new CreateType(*tCast), &deleter<CreateType>);
    }
 
    // a wrapper to deallocate an object of type T: all dtors are protected but ObjectFactory is a friend of all classes
    template<class T>
    static void deleter(T *t) { delete t; }
 
    static std::string errorMsg;
};
 
template<class CreateType>
class ObjectFactoryRegisterXMLNameHelper {
 
  public:
 
    ObjectFactoryRegisterXMLNameHelper(const MBXMLUtils::FQN &name) noexcept {
      try {
        ObjectFactory::registerXMLName<CreateType>(name);
      }
      catch(std::exception &ex) {
        ObjectFactory::addErrorMsg(ex.what());
      }
      catch(...) {
        ObjectFactory::addErrorMsg("Unknown error");
      }
    };
 
};
 
}
 
#define OPENMBV_OBJECTFACTORY_REGISTERXMLNAME(ThisType, name) \
  static OpenMBV::ObjectFactoryRegisterXMLNameHelper<ThisType> BOOST_PP_CAT(objectFactoryRegistrationDummyVariable_, __LINE__)(name);
 
 
#endif