RE: [boost] Re: Re: Policy or Trait?

From: David Bergman (davidb_at_[hidden])
Date: 2004-04-02 11:01:26

Gennadiy wrote (in response to my GP-ish classification): 

> -----Original Message-----
> From: boost-bounces_at_[hidden] 
> [mailto:boost-bounces_at_[hidden]] On Behalf Of Gennadiy Rozental
> Sent: Friday, April 02, 2004 12:58 AM
> To: boost_at_[hidden]
> Subject: [boost] Re: Re: Policy or Trait?
> 
> > > So, for me it is pretty easy, traits *only* describes 
> > > Model-invariant parts of Concept Features while policies furnish 
> > > Models of Concepts.
> >
> > Skipping all the GP stuff: traits DESCRIBE and policies ACT.
> 
> And why would we name these concepts Trait and Policy?

I ended with a simple discriminating rule to apply if one is insecure about
a particular notion being either a trait or a policy. It is not the
definition, i.e., it is not the case that *anything* that describes
something is a trait or that *anything* that act is a policy.
 
> Describe/Act classification could be interesting, but IMO it 
> has *nothing* to do with Trait/Policy one.

Not even as a discriminator? So, you do not agree that traits should always
describe a type or, more accurately, a Concept?

> See my other post 
> for one example. Here another
> one: how ConversionPolicy in SmartPointer design act?

I do not follow you.

> Let me repeat very simple rule (though a bit simplistic to be 
> correct in general case) I believe is keystone to the 
> Trait/Policy separation:
> 
> Trait is specific to the type
> Policy is orthogonal to the type.

If you read my original message, you will see that I classify trait as
specific to the "type," although the correct nomenclature would be that a
trait is specific to the Concept, in *positioning* the Model of a Concept in
the Feature Model corresponding to the Concept. That simple. So:

1. Trait is *both* specific to a "type" and descriptive.

In that same message, I stated that a policy furnishes, or decorates, a
Model of a Concept. That decoration can definitely be viewed as an
orthogonal aspect to the Model/Concept plane. Not that different from your
separation. Again, combining our views, we get:

2. Policy is *both* orthogonal to a "type" and behavioral.

What do you think about these combinations?

> Do you have an example refuting my view?

Yes, but I have to eat now. Will be back...

/David