Re: [boost] [type_traits] Interest in is_iterator type trait?

Subject: Re: [boost] [type_traits] Interest in is_iterator type trait?
From: Howard Hinnant (howard.hinnant_at_[hidden])
Date: 2014-08-19 12:38:10

On Aug 19, 2014, at 11:55 AM, Peter Dimov <lists_at_[hidden]> wrote:

> Beman Dawes wrote:
>> The intent was always to submit is_iterator to Boost, but we never got around to it. Now I need it in Boost.Filesystem, so I'd rather see it go in type traits than just sticking it into boost/filesystem/detail.
> 
> Out of curiosity, why do you need it? 

Fwiw, I used something closely related in libc++ for SFINAE on the “member template members” of the containers (the ones taking iterators) to disambiguate them from the members/constructors not taking iterators, but having the same number of parameters.  But instead of is_iterator, I needed is_input_iterator, is_forward_iterator, etc.  These refinements are implemented similar to what Beman shows, but takes into account which std iterator tag the nested iterator_category type is implicitly convertible to.

They can also be used instead of tag dispatching for the selection of an optimal algorithm.

Howard