Activator.CreateInstance for C++?

Question

In my .NET project, I have some code that creates new objects according to an xml. The Activator is the heart of what makes this possible. Is there a similar thing I can do in c++? I've found some IOC/DI frameworks, but I really don't need much functionality. The alternative is of course to simply write a switch, but that would need to be modified (along with the XML) each time I come up with a new type.

Answer 1

The coolest C++ implementation of a "superfactory" is one by my good friend Francis and you can find the article here on CodeProject.

I believe he wrote this factory with exactly this need in mind. It also powers his (de)serialization framework Daabli that reads plaintext C-style (and with some work - JSON, XML) files and recreates object graphs.

Hope this helps!

Answer 2

if you don't want a switch you roll your factory along these lines

#include <map>
#include <string>

class IHasCreate
{
};

typedef IHasCreate* (*CreateFunc)();

std::map<std::string,CreateFunc> factorymap;


class foo : IHasCreate
{
public:

    static IHasCreate* CreateFoo()
    {
        return new foo();
    }
};

class bar: IHasCreate
{
    public:
    static IHasCreate* CreateBar()
    {
        return new bar();
    }
};

IHasCreate* FactoryCreate( const std::string & name )
{
    return factorymap[name]();
}

int main()
{
    factorymap["foo"] = &foo::CreateFoo;
    factorymap["bar"] = &bar::CreateBar;


    IHasCreate *fooboject =  FactoryCreate("foo");
    IHasCreate *barboject =  FactoryCreate("bar");

    return 0;
}

The adding of stuff to the factorymap can be done by using some kind of macro magic that some people may find more appealing.

#include <map>
#include <string>

class IHasCreate
{
};

typedef IHasCreate* (*CreateFunc)();

std::map<std::string,CreateFunc> factorymap;

bool RegisterType( const std::string& type , CreateFunc func )
{
    factorymap[type] = func;
    return true;
}

IHasCreate* FactoryCreate( const std::string & name )
{
    return factorymap[name]();
}

#define REGISTER(type)  \
IHasCreate* type##createfunc() { return new type(); } \
bool type##temp = RegisterType( #type , &type##createfunc); 


class foo : public IHasCreate
{
};

REGISTER(foo);

class bar: public IHasCreate
{
};

REGISTER(bar);

int main()
{

    IHasCreate *fooboject =  FactoryCreate("foo");
    IHasCreate *barboject =  FactoryCreate("bar");

    return 0;
}