Re: [Boost-bugs] [Boost C++ Libraries] #10514: Cannot copy const sub_range to non-const

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #10514: Cannot copy const sub_range to non-const
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2015-02-02 02:27:40

#10514: Cannot copy const sub_range to non-const
-----------------------------------------+------------------------
  Reporter:  Braden McDaniel <braden@…>  |      Owner:  neilgroves
      Type:  Bugs                        |     Status:  reopened
 Milestone:  To Be Determined            |  Component:  range
   Version:  Boost 1.56.0                |   Severity:  Regression
Resolution:                              |   Keywords:
-----------------------------------------+------------------------
Changes (by Braden McDaniel <braden@…>):

 * status:  closed => reopened
 * resolution:  invalid =>

Comment:

 Replying to [comment:1 neilgroves]:
 > The propagation of const-ness is the rationale for having sub_range in
 addition to iterator_range. Please see:
 http://www.boost.org/doc/libs/1_57_0/libs/range/doc/html/range/reference/utilities/sub_range.html

 >
 > If you do not wish to propagate const-ness please use iterator_range
 instead.

 It appears to me that `const` is being propagating incorrectly in this
 case. At the very least, `const` is being propagated in a way that is
 inconsistent with how it is normally propagated with the standard
 containers. Consider the analogous example using just `std::vector`:
 {{{#!c++
 std::vector<int> v(10);
 const std::vector<int> & v_ref = v;
 std::vector<int> u = v_ref;
 }}}
 This compiles just fine because there is no problem copying a `const int`
 to an `int`. To the point: it doesn't matter that `v_ref` uses
 `const_iterator`s.

 (So, I may have framed the problem incorrectly in my initial description.
 The problem isn't that `const_iterator`s are being used at all; the
 problem is that `sub_range` seems to insist that the lhs use
 `const_iterator`s just because the rhs does.)

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/10514#comment:2>
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