[boost] Re: Policy or Trait?

From: Gennadiy Rozental (gennadiy.rozental_at_[hidden])
Date: 2004-04-02 11:22:44

> > And I think the same. IMO any example of trait/policy mixure in the
> > same class would be an example of bad design.
>
> I don't know; it seems to me that the
>
>   template <class T, class Policy = xxx_traits<T> >
>   class Foo;
>
> idiom might not be a bad one for some uses if xxx_traits is only
> supplying associated types.  It allows customization of the meaning of
> Foo<X> for any X by specializing xxx_traits<X>, while also allowing
> users to explicitly choose Foo<X, Y> when they don't like the default
> for X.

And you get basic_string design as a result.

If user do not like default value for the trait. It's value should be set
*externally* to the component definition. That is the major point I am
trying to prove in regards to numeric_cast design and in thic generic
discussion.

Gennadiy.