Hello David, Thursday, May 10, 2007, 2:49:56 PM, you wrote:
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.
Well... I guess I could use iterator_adaptor in some cases and I can't remember why I didn't in other. Thanks for the pointer.
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.
I agree that the case is rather specific, though I think such template could still be handy here and there. Since I don't have any striking examples of use right now and a little bit short in time, I'll leave it to some day when I have either of them. :) -- Best regards, Andrey mailto:andysem@mail.ru