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

Subject: [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: 2011-06-24 21:42:20

#5641: Multiple keys in same index for same value in multi_index
--------------------------------------------+-------------------------------
 Reporter:  Aaron Moss <moss.aaron@…>       |       Owner:  joaquin       
     Type:  Feature Requests                |      Status:  new           
Milestone:  To Be Determined                |   Component:  multi_index   
  Version:  Boost 1.46.1                    |    Severity:  Not Applicable
 Keywords:                                  |  
--------------------------------------------+-------------------------------
 I have a collection of data objects analogous to this one:

 {{{#!c++
 struct foo {
   bar b;
   std::set<baz> s;
   quux q;
 };
 }}}

 which I want to be able to efficiently search either by b, or any element
 of s (q is extra information). The natural way to do that would be some
 sort of multi_index-like container, where I have a hash-map of bar to foo
 (with one key per value), and another hash-map of baz to foo (with
 multiple keys mapping to the same foo).

 I may be mistaken, but I don't believe the second map can be set up
 (efficiently, in its obvious implementation) in the current multi_index.
 However, if it is allowable to have different sizes for different views of
 the same collection / different numbers of keys of the same index mapping
 to the same value, it would perhaps be a useful capability.

 Without looking at the Boost sources, this would probably involve
 generalizing key extractors to support multiple keys from the same value,
 with syntax looking something like the following:

 {{{#!c++
 typedef multi_index_container<
   foo,
   indexed_by<
     hashed_unique<
       member<foo, bar, &foo::b>
     >,
     hashed_unique<
       member_collection<foo, std::set<baz>::iterator, &foo::s.begin,
 &foo::s.end>
     >
   >
 > my_map;
 }}}

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