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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.


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