??? ??? ??? ????? ??? ??????? ??? ??????

??? ???? BaseFactory ???? ??? ?? ???? ??? ?????. ??? ??? ???? ???? ???? ???. ??? ?????? ??? ? Derived ???? ?? if ?? ???? ???? ???. C#? Reflection ??? ??? ??? ??? ?? ??? ?? ??? ??? ??? ?? ????.

????? ???? ????? ????

???? C?? ????? ????. ??? ? ??? ??? ?? ?? ??? ?? ????. ??? ?? ??? ???? ?? ?????.

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template<typename T> Base * createInstance() { return new T; }

typedef std::map<std::string, Base*(*)()> map_type;

map_type map;
map["DerivedA"] = &amp;createInstance<DerivedA>;
map["DerivedB"] = &amp;createInstance<DerivedB>;

??? ??? ?????? ? ????. ???:

return map[some_string]();

?? ??

?? ???? ??? ??? ????? ???? ????.

// w base.hpp:
template<typename T> Base * createT() { return new T; }

struct BaseFactory {
    typedef std::map<std::string, Base*(*)()> map_type;

    static Base * createInstance(std::string const&amp; s) {
        map_type::iterator it = getMap()->find(s);
        if(it == getMap()->end())
            return 0;
        return it->second();
    }

protected:
    static map_type * getMap() {
        // nigdy nie usuwane (istnieje do zakończenia programu)
        // poniewa? nie mo?emy zagwarantowa? poprawnej kolejno?ci usuwania
        if(!map) { map = new map_type; }
        return map;
    }

private:
    static map_type * map;
};

template<typename T>
struct DerivedRegister : BaseFactory {
    DerivedRegister(std::string const&amp; s) {
        getMap()->insert(std::make_pair(s, &amp;createT<T>));
    }
};

// w derivedb.hpp
class DerivedB {
    ...;
private:
    static DerivedRegister<DerivedB> reg;
};

// w derivedb.cpp:
DerivedRegister<DerivedB> DerivedB::reg("DerivedB");

???? ??? ?? ????. ?? ??:

#define REGISTER_DEC_TYPE(NAME) \
    static DerivedRegister<NAME> reg

#define REGISTER_DEF_TYPE(NAME) \
    DerivedRegister<NAME> NAME::reg(#NAME)

?? ?? ???? ???? ?? ??? ?? ??? ??? ? ????. ??? ?? ??? Boost::variant:

typedef boost::variant<Foo, Bar, Baz> variant_type;
template<typename T> variant_type createInstance() {
    return variant_type(T());
}

typedef std::map<std::string, variant_type (*)()> map_type;

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