Re: Dynamically choosing what to "new"

Pat wrote:


It is common.

I don't know of any other generic factory implementations but the one in
Austria C++ will allow you to register a number of different factories
(named Dog, Cat etc) and simply request construction on an appropriate one.

#include "at_factory.h"

class Animal
{

};

int main( int argc, char ** argv )
{

    if ( argc == 2 )
    {

       Animal * animal = at::FactoryRegister<
                Animal, at::DKy
             >::Get().Create( argv[1] )();

       // the Create method takes a few other arguments
       // one that tells it to throw on failure
       if ( ! animal )
       {
          return 1;
       }

    }
};

// this stuff below can be in any source file or even DLL/DSO

struct Dog : Animal
{
};

// AT_MakeFactory0P is a macro that "registers" a factory
// for Dog under the key "Dog" over it's interface Animal
// using a key type of at::DKy - you could use std::string
// here if you wanted to.
AT_MakeFactory0P( "Dog", Dog, Animal, at::DKy );

struct Cat : Animal
{
};

AT_MakeFactory0P( "Dog", Cat, Animal, at::DKy );

Careful that you make sure the factory object files are linked in.
That's the usual source of frustration using this. There are a couple
of tools which help you do that but it's the only issue.