From: Andy Little (andy_at_[hidden])
Date: 2004-04-04 05:42:17
"David Abrahams" <dave_at_[hidden]> wrote
> "Andy Little" <andy_at_[hidden]> writes:
> > "David Bergman" <davidb_at_[hidden]> wrote
> >> David A. wrote:
> >> > "Andy Little" <andy_at_[hidden]> writes:
> > [snip]
> >> > > Surely a trait is *part of the *definition* * of an *entity* in a
> >> > > wider sense.
> >> >
> >> > I think I just quite definitively disagreed with that
> >> > assertion already ;^)
> >> Would you disagree with Andy even if that "wider sense" was a GP
> > I guess that David Abrahams is taking me to task on use of the word
> > which is defined in the standard (3-3).
> No, I'm not. Just read the words I wrote. I simply reject the idea
> that a trait specialization is part of the definition of the type(s)
> it applies to.
hmm ..From the latest qualifications of your objections above I now assume
you are seeing this.
Where traits is the subject, traits<T> is Not part of T's definition.
But we have been discussing numeric::converter and std::basic_string and
differences between traits and policies... I have been seeing this :
template <typename T>
typedef traits<T> arg_traits;
Where T1 is the subject, traits<T> Is part of T1's definition. Also see
standard 21-2 relating to strings. " <strings> ..need a set of related
types... to complete the definition of their semantics".
The traits or policy discussion seems to boil down to this:
In T1 above arg_traits is not user modifiable, However
template <typename T,typename P>
typedef P arg_traits;
arg_traits in T2 is user-modifiable. traits<T> is a traits-class, but
traits<T> could theoretically be used in T2, in which case it would be
regarded as implementing a policy. To implement various policies one can
define different traits-classes on the same type, however they might then be
best referred to as policy-classes. Use of traits<T> in T1 could also be
regarded as a policy, but an immutable one. Based on that one could say that
a policy is implemented, simply the Use of a traits-class or a
policy-class. The term policy being useful only if the policy is modifiable.
Boost list run by bdawes at acm.org, gregod at cs.rpi.edu, cpdaniel at pacbell.net, john at johnmaddock.co.uk