Gennadiy wrote (in response to my GP-ish classification):
-----Original Message----- From: boost-bounces@lists.boost.org [mailto:boost-bounces@lists.boost.org] On Behalf Of Gennadiy Rozental Sent: Friday, April 02, 2004 12:58 AM To: boost@lists.boost.org 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