Re: [boost] Re: Policy or Trait?

From: Rob Stewart (stewart_at_[hidden])
Date: 2004-04-02 11:36:08

From: David Abrahams <dave_at_[hidden]>
> 
> 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.

Right.  The only problem arises when xxx_traits is used as the
exemplar for the policy and not all of xxx_traits' interface is
needed.  That can be solved with documentation, but the tendency
is likely to be to copy xxx_traits and modify its functionality
when creating a new policy class.

-- 
Rob Stewart                           stewart_at_[hidden]
Software Engineer                     http://www.sig.com
Susquehanna International Group, LLP  using std::disclaimer;