[boost] Re: Policy or Trait?

From: David Abrahams (dave_at_[hidden])
Date: 2004-04-02 15:04:24

"Gennadiy Rozental" <gennadiy.rozental_at_[hidden]> writes:

>> > I do undersand that. But I still believe that trait specification is
> part of
>> > definition.
>>
>> Not if you want to describe the properties of some 3rd-party class:
>>
>>     #include <3rd_party/smart_ptr.hpp>
>>
>>     template <class T>
>>     struct is_dereferenceable<third_party::smart_ptr<T> >
>>        : mpl::true
>>     {};
>
> I imagine you wouldn't do it 10 times in your code and most definetlety you
> wouln't define it differently in different headers. Most probable you
> introduce 3rd_party_smart_ptr_wrap.hpp that contains above trait
> specification and use everywhere instead of 3rd_party/smart_ptr.hpp. So in
> this case from my POV you *updated* smart_ptr definition and use this
> updated definition instead of original one.

So if I write a free function that accepts third_party::smart_ptr<T>
arguments I'm also updating the smart_ptr definition?

You must have a funny definition of "definition".

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com