[boost] Re: Canonical form for Type Traits specializations?

From: Eric Friedman (ebf_at_[hidden])
Date: 2003-11-27 23:38:44

David Abrahams wrote:
> Eric Friedman <ebf_at_[hidden]> writes:
> 
> 
>>It seems to me the standard form of such a specialization would look
>>as follows:
>>
>>// ...at file scope...
>>namespace boost {
>>
>>   template <>
>>   struct has_nothrow_copy< myUDT >
>>     : mpl::true_
>>   {
>>   };
>>
>>}
>>
>>The problem I see here is this approach (needlessly) forces MPL upon
>>the user.
> 
> 
> It's not needless.  You're going to force *something* upon the user.
> Why not boost/mpl/bool.hpp?
> 

But why? The type traits library should have nothing to do with MPL (at 
least from a user's perspective).

>> 1) Provide a typedef of boost::mpl::true_ named boost::true_, or
>>    perhaps boost::tt_true to keep it Type Traits-specific. (I suppose
>>    we could do the same for false_.)
> 
> 
> What problem is this solving?  Just that they don't have to write the
> letters "mpl"?

Yes. I believe it is confusing for a user who is seeking simply to 
specialize a type trait to have to think about an unrelated library.

I think maybe we should have boost::integral_constant (a la TR1) instead 
of boost::mpl::integral_c, boost::mpl::bool_, etc.

I do want to be reasonable though: this isn't a critical issue. It just 
seems to me we'd want to clear it up now if possible so we aren't stuck 
with it later.

Eric