[Boost-bugs] [Boost C++ Libraries] #11346: Segment iterator does not work with ranges returning values instead of references

Subject: [Boost-bugs] [Boost C++ Libraries] #11346: Segment iterator does not work with ranges returning values instead of references
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2015-05-26 17:00:32

#11346: Segment iterator does not work with ranges returning values instead of
references
------------------------------+---------------------------
 Reporter:  eveith@…          |      Owner:  barendgehrels
     Type:  Bugs              |     Status:  new
Milestone:  To Be Determined  |  Component:  geometry
  Version:  Boost 1.57.0      |   Severity:  Problem
 Keywords:                    |
------------------------------+---------------------------
 The Boost.Geometry segment iterator does not work with ranges/custom
 iterators that return a value instead of a reference when dereferenced.

 The problem surfaced with the adaption of GDAL/OGR's geometry classes to
 Boost.Geometry. All OGRSimpleCurve descendants (e.g., OGRLineString) have
 only "copy-out" access to their points:

 {{{
 int         getNumPoints() const { return nPointCount; }
 void        getPoint( int, OGRPoint * ) const;
 double      getX( int i ) const { return paoPoints[i].x; }
 double      getY( int i ) const { return paoPoints[i].y; }
 double      getZ( int i ) const;
 }}}

 The defeats the notion of a iterator de-reference operation that returns a
 reference to the OGRPoint underlying a given OGRLineString. Thus, the
 `iterator_facade`-implementing iterator adapter returns a value and not a
 reference.

 However, the attached test-case provided by Menelaos Karavelas fails to
 properly iterate segments of a given linestring and produces the following
 output:

 {{{
 geometry: LINESTRING(1 1,2 2,3 3,4 4,9 9)
 points: (1, 1) (2, 2) (3, 3) (4, 4) (9, 9)
 segments: ((2.0872e-317, 6.95257e-310), (6.91222e-310, 6.91222e-310))
 ((2.0872e-317, 6.95257e-310), (6.91222e-310, 6.91222e-310)) ((2.0872e-317,
 6.95257e-310), (6.91222e-310, 6.91222e-310)) ((2.0872e-317, 6.95257e-310),
 (6.91222e-310, 6.91222e-310))
 }}}

 The full iterator/adaptor code is located at https://github.com/eveith

 /ogr-boost-adapter.

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/11346>
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