boost :: Funktions hat eine Fabrik Vorlage, die sehr flexibel ist: http://www.boost.org/doc/libs/1_54_0/libs/functional/factory/doc/html/index.html
obwohl Meine Präferenz ist Wrapper-Klassen zu erzeugen, die die Zuordnung und Objekterstellung Mechanismus verstecken. Das übliche Szenario, dem ich begegne, ist die Notwendigkeit, verschiedene abgeleitete Klassen einer Basisklasse Schlüsseln zuzuordnen, wobei die abgeleiteten Klassen alle eine gemeinsame Konstruktorsignatur zur Verfügung haben. Hier ist die Lösung, die ich bisher gefunden habe.
#ifndef GENERIC_FACTORY_HPP_INCLUDED
//BOOST_PP_IS_ITERATING is defined when we are iterating over this header file.
#ifndef BOOST_PP_IS_ITERATING
//Included headers.
#include <unordered_map>
#include <functional>
#include <boost/preprocessor/iteration/iterate.hpp>
#include <boost/preprocessor/repetition.hpp>
//The GENERIC_FACTORY_MAX_ARITY directive controls the number of factory classes which will be generated.
#ifndef GENERIC_FACTORY_MAX_ARITY
#define GENERIC_FACTORY_MAX_ARITY 10
#endif
//This macro magic generates GENERIC_FACTORY_MAX_ARITY + 1 versions of the GenericFactory class.
//Each class generated will have a suffix of the number of parameters taken by the derived type constructors.
#define BOOST_PP_FILENAME_1 "GenericFactory.hpp"
#define BOOST_PP_ITERATION_LIMITS (0,GENERIC_FACTORY_MAX_ARITY)
#include BOOST_PP_ITERATE()
#define GENERIC_FACTORY_HPP_INCLUDED
#else
#define N BOOST_PP_ITERATION() //This is the Nth iteration of the header file.
#define GENERIC_FACTORY_APPEND_PLACEHOLDER(z, current, last) BOOST_PP_COMMA() BOOST_PP_CAT(std::placeholders::_, BOOST_PP_ADD(current, 1))
//This is the class which we are generating multiple times
template <class KeyType, class BasePointerType BOOST_PP_ENUM_TRAILING_PARAMS(N, typename T)>
class BOOST_PP_CAT(GenericFactory_, N)
{
public:
typedef BasePointerType result_type;
public:
virtual ~BOOST_PP_CAT(GenericFactory_, N)() {}
//Registers a derived type against a particular key.
template <class DerivedType>
void Register(const KeyType& key)
{
m_creatorMap[key] = std::bind(&BOOST_PP_CAT(GenericFactory_, N)::CreateImpl<DerivedType>, this BOOST_PP_REPEAT(N, GENERIC_FACTORY_APPEND_PLACEHOLDER, N));
}
//Deregisters an existing registration.
bool Deregister(const KeyType& key)
{
return (m_creatorMap.erase(key) == 1);
}
//Returns true if the key is registered in this factory, false otherwise.
bool IsCreatable(const KeyType& key) const
{
return (m_creatorMap.count(key) != 0);
}
//Creates the derived type associated with key. Throws std::out_of_range if key not found.
BasePointerType Create(const KeyType& key BOOST_PP_ENUM_TRAILING_BINARY_PARAMS(N,const T,& a)) const
{
return m_creatorMap.at(key)(BOOST_PP_ENUM_PARAMS(N,a));
}
private:
//This method performs the creation of the derived type object on the heap.
template <class DerivedType>
BasePointerType CreateImpl(BOOST_PP_ENUM_BINARY_PARAMS(N,const T,& a))
{
BasePointerType pNewObject(new DerivedType(BOOST_PP_ENUM_PARAMS(N,a)));
return pNewObject;
}
private:
typedef std::function<BasePointerType (BOOST_PP_ENUM_BINARY_PARAMS(N,const T,& BOOST_PP_INTERCEPT))> CreatorFuncType;
typedef std::unordered_map<KeyType, CreatorFuncType> CreatorMapType;
CreatorMapType m_creatorMap;
};
#undef N
#undef GENERIC_FACTORY_APPEND_PLACEHOLDER
#endif // defined(BOOST_PP_IS_ITERATING)
#endif // include guard
Ich bin generell gegen schwere Makro-Verwendung, aber ich habe hier eine Ausnahme gemacht. Der obige Code generiert GENERIC_FACTORY_MAX_ARITY + 1 Versionen einer Klasse mit dem Namen GenericFactory_N, für jede N zwischen 0 und GENERIC_FACTORY_MAX_ARITY inklusive.
Die Verwendung der generierten Klassenvorlagen ist einfach. Angenommen, Sie möchten eine Factory, die abgeleitete BaseClass-Objekte mithilfe einer Zeichenfolgenzuordnung erstellt. Jedes der abgeleiteten Objekte benötigt 3 ganze Zahlen als Konstruktorparameter.
#include "GenericFactory.hpp"
typedef GenericFactory_3<std::string, std::shared_ptr<BaseClass>, int, int int> factory_type;
factory_type factory;
factory.Register<DerivedClass1>("DerivedType1");
factory.Register<DerivedClass2>("DerivedType2");
factory.Register<DerivedClass3>("DerivedType3");
factory_type::result_type someNewObject1 = factory.Create("DerivedType2", 1, 2, 3);
factory_type::result_type someNewObject2 = factory.Create("DerivedType1", 4, 5, 6);
Der Klassen-Destruktor GenericFactory_N ist virtuell, um Folgendes zu ermöglichen.
class SomeBaseFactory : public GenericFactory_2<int, BaseType*, std::string, bool>
{
public:
SomeBaseFactory() : GenericFactory_2()
{
Register<SomeDerived1>(1);
Register<SomeDerived2>(2);
}
};
SomeBaseFactory factory;
SomeBaseFactory::result_type someObject = factory.Create(1, "Hi", true);
delete someObject;
Beachten Sie, dass diese Zeile des generischen Fabrik Generator Makro
#define BOOST_PP_FILENAME_1 "GenericFactory.hpp"
nimmt die generische Werk Header-Datei benannt wird GenericFactory.hpp
seine teilweise möglich, mit C++ 0x und variadic templates .. – smerlin