Re: [Boost-bugs] [Boost C++ Libraries] #5641: Multiple keys in same index for same value in multi_index

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #5641: Multiple keys in same index for same value in multi_index
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2011-07-05 14:08:21

#5641: Multiple keys in same index for same value in multi_index
---------------------------------------------+------------------------------
  Reporter:  Aaron Moss <moss.aaron@…>       |       Owner:  joaquin       
      Type:  Feature Requests                |      Status:  closed        
 Milestone:  To Be Determined                |   Component:  multi_index   
   Version:  Boost 1.46.1                    |    Severity:  Not Applicable
Resolution:  wontfix                         |    Keywords:                
---------------------------------------------+------------------------------
Changes (by joaquin):

  * status:  new => closed
  * resolution:  => wontfix

Comment:

 Hi Aaron,

 The idea you propose is in direct contradiction with many basic
 assumptions about the kind of data structures Boost.MultiIndex is designed
 to generate: for one, all indices have the same size(), meaning that a
 particular element appears once and exactly once in each index. Breaking
 these basic assumption subvert the whole internal infrastucture of the
 library, and it is not easy to see how this could be done in a
 conceptually sound manner. In other words, I don't plan to augment
 Boost.MultiIndex the way you propose.

 You can approximate your scenario with some manual work: instead of
 storing plain foos use some kind of proxy like

 {{{
 struct foo_proxy
 {
   boost::shared_ptr<foo> p;
   boost::function<const baz&(const foo&)> key;
 };
 }}}

 where p points to the actual element and key is a key extractor settable
 at run time. Then, for each element x insert as many proxys as elements
 has its s member, setting for each the appropriate key extractor returning
 the i-th element of x.s. A collateral effect is that indices other than
 the used for s will contain duplicates as well.

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/5641#comment:1>
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