[Boost-bugs] [Boost C++ Libraries] #5659: The closed_plus structure should accept a custom infinity value.

Subject: [Boost-bugs] [Boost C++ Libraries] #5659: The closed_plus structure should accept a custom infinity value.
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2011-06-29 14:11:09

#5659: The closed_plus structure should accept a custom infinity value.
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 Reporter:  Thomas Sewell <thomas.sewell@…>             |       Owner:  asutton
     Type:  Bugs                                        |      Status:  new    
Milestone:  To Be Determined                            |   Component:  graph  
  Version:  Boost 1.46.1                                |    Severity:  Problem
 Keywords:                                              |  
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 I'm trying to run dijkstra_shortest_paths with a custom distance type (my
 graph supports two metrics, I want to find the length in metric A of the
 shortest paths according to metric B).

 I've been struggling to understand why I was getting dependencies on
 MyDistType(int). It turns out that overloading + on MyDistType is only
 half the story. The default combine operator for distances comes from
 closed_plus, which assumes an infinity value can be constructed by
 std::numeric_limits<D>::max(). This function seems to degrade to trying
 the constructor T(n) for some int n (probably INT_MAX) if it isn't a known
 numeric type, leading to bizarre errors (buried under piles of template
 goop).

 This patch gives instances of closed_plus a parameter to store the custom
 infinity value, defaulting to the one from std::numeric_limits. It also
 passes the correct default value in dijkstra_shortest_paths. I haven't
 checked whether any of the other algorithms that use closed_plus can
 potentially have non-standard infinity values.

 Hope you agree this is an improvement.

 Yours,
     Thomas.

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/5659>
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