Re: [boost] Re: Policy-based designs considered harmful?

From: Greg Colvin (gcolvin_at_[hidden])
Date: 2002-01-23 17:33:45

From: "Tim Woodard" <timw_at_[hidden]>
To: <boost_at_[hidden]>
Sent: Wednesday, January 23, 2002 9:27 AM
Subject: [boost] Re: Policy-based designs considered harmful?

> "David Abrahams" <david.abrahams_at_r...> wrote:
> ...
> > I think things get much trickier with generative programming, where
> all of
> > the configurations tend to be determined by the library, but there may
> be
> > thousands of them. The Boost Graph Library's adjacency_list is more
> like a
> > generative design than a policy-based one, and I think that approach
> places
> > a much higher testing burden on the library writer. This is mostly due
> to
> > the fact that generative designs tend toward a single monolithic
> component
> > (or component generator) which manages all the complexity behind its
> facade.
> > A policy-based approach breaks the design into smaller pieces which
> can be
> > verified separately.
> 
> One thing I've been working on is applying generative programming as
> "front-end" for a policy-based design.  In C&E, generative programming
> is used in conjunction with the GenVoca architecture.  Using it in
> conjunction with policies, I think, is more natural.  With this
> approach, the generator takes user-supplied options and selects
> appropriate the policies.  Testing the library combinations actually
> becomes simpler because the combinations are limited by the generator.
> The generator itself can easily be tested by verifying at compile-time
> that specified option configurations result in the expected policies
> being selected.

Sounds like the best of both worlds.