RE: [boost] Policy or Trait?

From: Rozental, Gennadiy (gennadiy.rozental_at_[hidden])
Date: 2004-04-01 17:12:19

> Trait - A class template parameterized on a single type that 
> associates information with that type.  A traits class, 
> therefore, provides an external, named grouping of 
> metainformation, behavior, or both for that type.  A trait 
> class is never passed as a template parameter; it's name is 
> ubiquitous. A traits class never has state.

By state you mean non-static data members, yes?

> Policy - A class template passed to other templates for the 
> purpose of providing a named grouping of metainformation, 
> behavior, or both to those templates.  Because it is a 
> template parameter, different policy classes can be used as 
> desired.  In many cases, a policy class is used as a base class.

Well, apparently there is somebody who think the same as I do. 

Thank you Rob, for your definitions. They seems sound and close to what I
have in mind.
 
> What do you think?  I know that my definitions mean that 
> std::char_traits is a policy class, despite its name, and 
> they probably deviate from some other ad hoc definitions.  
> The question is whether these provide sound, distinct, and 
> defensible concepts that could be codified for future use at 
> Boost (and elsewhere).

That's flaw in char_traits not in definitions above, IMO.

Gennadiy.