Re: Dynamically choosing what to "new"

Gianni Mariani <>
Sat, 09 Jun 2007 21:02:36 +1000
Pat wrote:


I've run into a strange problem, but one that seems like it might be
fairly common.

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.

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