Re: [boost] Interest in a small array count facility?

From: David Abrahams (dave_at_[hidden])
Date: 2006-06-29 14:55:09

Gennaro Prota <gennaro_prota_at_[hidden]> writes:

> * Any reason why you used mpl::identity<empty> instead
>   of mpl::identity<>? 

a. I didn't know identity had a default argument

b. I'm not sure identity<> is supposed to be equivalent to
   identity<empty>

>   does the latter break on some known
>   compiler? I'm asking because it could be the reverse and
>   that using the default (i.e. boost::mpl::na) is the
>   preferred/most reliable way.
>
>   My guess is that you just wanted to have a clearer
>   diagnostic message, but I wanted to ask.

It doesn't help with the diagnostic.  Either the nested thing fails to
have a ::not_an_array member and you get an error, or it has the member
and you don't.

And, note, I didn't use ::type because that confuses the compiler with
boost::type<...> and the resulting error message is less clear than it
would be otherwise.

Enclosed is one easy simplification step.



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