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

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

?? 1: ???? ??? ?? ??

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

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

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

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

return map[some_string]();

?? 2: ??? ?? ??

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

struct BaseFactory {
    static Base * createInstance(std::string const& s) {
        auto it = getMap()->find(s);
        return it != getMap()->end() ? it->second() : nullptr;
    }

    static std::map<std::string, std::function<Base*()>> * getMap() {
        if (!map) { map = new std::map<std::string, std::function<Base*()>>; }
        return map;
    }

private:
    static std::map<std::string, std::function<Base*()>> * map;
};

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

class DerivedB {
private:
    static DerivedRegister<DerivedB> reg("DerivedB");
};

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

?? 3: Boost Variant

?? ?? ???? ?? ?? ?? ???? ?? Boost ?? ?????? ??? ? ????.

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;

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

????? C?? ??? ?? ????? ?? ?????? ?? ?? ????? ?????. ??? ???, ??? ?? ?? Boost ?? ?????? ???? ??? ??? ?? ? ????.

? ??? ??? ?? ????? C ??? ??? ?????? ? ?????? ?? ?????. ??? ??? PHP ??? ????? ?? ?? ??? ?????!