Object factory using Boost.Phoenix, Boost.Function and Boost.SmartPtr libraries

factory.cpp

#include <boost/foreach.hpp>
#include <boost/function.hpp>
#include <boost/spirit/include/phoenix.hpp>
#include <boost/variant.hpp>
#include <iostream>
#include <map>
#include <string>
#include <vector>

struct Object1 { std::string hello() const { return "Hi, Object1"; } };
struct Object2 { std::string hello() const { return "Ay, Object2"; } };
struct Object3 { std::string hi() const { return "Oh, hi!"; } };

struct bad_type_exception : std::exception {
    char const * what() const throw() { return "No such class!"; }
};

typedef boost::variant<Object1, Object2, Object3> Object;

struct HelloVisitor {
    typedef std::string result_type;
    template <typename T> std::string operator()(T const & t) {
        return t.hello(); // <-- A templated solution will handle these guys.
    }
    std::string operator()(Object3 const & t) {
        return t.hi(); // <-- But he's a bit different, you see...  ;-)
    }
};

struct Factory {
    typedef std::map<std::string, boost::function<Object()> > FactoryMap;
    FactoryMap f;
    Factory() {
        using boost::phoenix::construct;
        f["Object1"] = construct<Object1>();
        f["Object2"] = construct<Object2>();
        f["Object3"] = construct<Object3>();
        // ...
    }
    Object operator()(std::string const & type) const {
        FactoryMap::const_iterator it = f.find(type);
        if (it == f.end()) throw bad_type_exception();
        return it->second();
    }
};

int main() {
    Factory factory;
    std::vector<std::string> types;
    types.push_back("Object1");
    types.push_back("Object3");
    types.push_back("Object2");
    std::vector<Object> items;
    BOOST_FOREACH(std::string const & type, types)
        items.push_back(factory(type));
    HelloVisitor hello;
    BOOST_FOREACH(Object const & item, items)
        std::cout << boost::apply_visitor(hello, item) << std::endl;
    // Prints:
    //  Hi, Object1
    //  Oh, hi!
    //  Ay, Object2
}

See also "improved" version with even more Phoenix stuff, in https://gist.github.com/1054616.