Re: [Boost-bugs] [Boost C++ Libraries] #11113: Support easy enumeration of all elements with BOOST_FOREACH

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #11113: Support easy enumeration of all elements with BOOST_FOREACH
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2015-04-04 18:47:21

#11113: Support easy enumeration of all elements with BOOST_FOREACH
-------------------------------------+-------------------------------------
  Reporter:  Thomas Trummer          |      Owner:  awulkiew
  <th.trummer@…>                     |     Status:  closed
      Type:  Feature Requests        |  Component:  geometry
 Milestone:  To Be Determined        |   Severity:  Cosmetic
   Version:  Boost 1.57.0            |   Keywords:  rtree, iterator, range,
Resolution:  fixed                   |  for
-------------------------------------+-------------------------------------
Changes (by awulkiew):

 * keywords:   => rtree, iterator, range, for
 * status:  new => closed
 * resolution:   => fixed

Comment:

 Thanks for the suggestion!

 Boost.Foreach and Boost.Range is now supported in develop branch and will
 be in Boost 1.59. I added `const_iterator`, `begin()` and `end()` members
 to the rtree. The category of iterator is ForwardIterator so the rtree is
 now adapted to (const) ForwardRange concept. It should be possible to
 adapt it to BidirectionalRange so if this was needed, just let me know.

 Unfortunately the thing with `queried()` adaptor is more complicated.
 Currently it isn't a lazy-range but a container (wrapped `std::vector`).
 If it was used to iterate over all values stored in the rtree all of them
 would be copied into this container. I probably shouldn't change it to
 lazy-range now since currently it's a RandomAccessRange so e.g. it can be
 sorted, etc. A lazy-range would be ForwardRange, this could be a breaking
 change. But if you think it should be done please write a suggestion e.g.
 on the mailing list so we could discuss. I plan to fix it by implementing
 the "new" `view::query()` and `cont::query()` adaptors (currently a
 proposal so I'm waiting for the committee to know what names I could use)
 and deprecating the `queried()` adaptor.

 For now (Boost <= 1.58) I propose a workaround. You could create a range
 representing all of the values stored in the rtree by yourself. You need
 to pass `bgi::satisfies()` predicate with a UnaryFunction always returning
 `true` into `qbegin()`. Well, there may be a problem, until now
 `const_query_iterator` was InputIterator. This might cause problems in
 some cases, e.g. related to Boost.Range concept checks. Besides the change
 you proposed I also upgraded `const_query_iterator` to ForwardIterator.
 But, I think that something like this could work:

 {{{
 struct always_true
 {
     template <typename T>
     bool operator()(T const&) const { return true; }
 };

 // Return a range containing all Rtree elements
 template <typename Rtree>
 std::pair
     <
         typename Rtree::const_query_iterator,
         typename Rtree::const_query_iterator
     >
 all(Rtree const& tree)
 {
     return std::make_pair(tree.qbegin(bgi::satisfies(always_true())),
                           tree.qend());
 }

 /*...*/

 BOOST_FOREACH(point2_t const& pt, all(tree))
 {
     // ...
 }

 }}}

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/11113#comment:2>
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