on Wed May 09 2007, Andrey Semashev <andysem-AT-mail.ru> wrote:
Hello David,
Wednesday, May 9, 2007, 8:27:53 PM, you wrote:
on Tue May 08 2007, Andrey Semashev <andysem-AT-mail.ru> wrote:
Hello,
Quite often I find myself writing an is_const_iterator trait which looks like this:
[snip]
Maybe it is worth adding to Boost.Iterators library? Or maybe there already is something like that?
What's it useful for?
Mostly I used it to implement my iterators for some adopted STL-like containers. It shortens the iterator_facade template parameters list:
template< NodeItT > struct MyIterator : public iterator_facade< MyIterator< NodeItT >, typename mpl::if_< is_const_iterator< NodeItT >, const value_type, value_type >::type, typename iterator_category< NodeItT >::type > { };
Is there some good reason you're not using iterator_adaptor here? This looks like a classic use case for it. That would eliminate the need for is_const_iterator in this case.
Another use case is different iterators translation to each other. It came handy when I had to implement something like multi_index_container iterator projecting:
template< int Index, typename SrcItT > typename mpl::if_< is_const_iterator< SrcItT >, typename nth_index< Index >::const_iterator, typename nth_index< Index >::iterator
::type project(SrcItT it);
I see. Well, I'm ambivalent. To me it doesn't look like that particular use case is worth doing much work to extend the library for, but if you can supply the implementation along with doc patches and tests, I guess I would be inclined to accept them. -- Dave Abrahams Boost Consulting http://www.boost-consulting.com Don't Miss BoostCon 2007! ==> http://www.boostcon.com