How would one typically create a dynamic factory method in PHP? By dynamic factory method, I mean a factory method that will autodiscover what objects there are to create, based on some aspect of the given argument. Preferably without registering them first with the factory either. I'm OK with having the possible objects be placed in one common place (a directory) though.

I want to avoid your typical switch statement in the factory method, such as this:

public static function factory( $someObject )
{
    $className = get_class( $someObject );
    switch( $className )
    {
        case 'Foo':
            return new FooRelatedObject();
            break;
        case 'Bar':
            return new BarRelatedObject();
            break;
        // etc...
    }
}

My specific case deals with the factory creating a voting repository based on the item to vote for. The items all implement a Voteable interface. Something like this:

Default_User implements Voteable ...
Default_Comment implements Voteable ...
Default_Event implements Voteable ...

Default_VoteRepositoryFactory
{
    public static function factory( Voteable $item )
    {
        // autodiscover what type of repository this item needs
        // for instance, Default_User needs a Default_VoteRepository_User
        // etc...
        return new Default_VoteRepository_OfSomeType();
    }
}

I want to be able to drop in new Voteable items and Vote repositories for these items, without touching the implementation of the factory.