Re: [boost] functional abstract factory or virtual constructor

From: Stathi Triadis (stathie_at_[hidden])
Date: 2008-03-02 12:33:10

On Fri, Feb 29, 2008 at 7:47 PM, Tobias Schwinger <tschwinger_at_[hidden]>
wrote:

>
> > I'm writing to gauge interest in an 'abstract factory',
> > very similar to the recently accepted functional/factory.
>
> Why not simply use factory/function combination?
>
>     typedef boost::function< A*(string, int) > AFactory;
>     typedef boost::factory< B* > BFactory;

That's quite nice... I didn't know you could do that. But this is no good
for modularization, correct?

Please note that in this case, BFactory is the "concrete factory" but it
>  does not know about that role. It's "virtualized from the outside".
>
> [...]
>
> For the transform you might get away without the dynamic call (that is
> if you don't need type erasure on the factory for modularization):

This was actually half the motivation for creating abstract_factory. I
needed
a way of reducing cyclic linker dependencies (VC++). A simple way
of doing that is to virtualize methods, but of course you can't do that for
constructors. I needed a virtual constructor of some sort.

The other reason came from working with the Loki::AbstractFactory
but becoming frustrated with not being able to pass parameters into the
Create
method. abstract_factory can be used a a component to create a
Loki::AbstractFactory without this limitation.

I've put abstract_factory.hpp in the vault if you'd like to take a look,
along
with an example that uses Loki::AbstractFactory, here:

http://www.boost-consulting.com/vault/index.php?action=downloadfile&filename=abstract_factory.zip&directory=&

Cheers,
Stathi