ceph/src/boost/libs/bimap/doc/html/boost_bimap/rationale/additional_features.html

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  25 <div class="section boost_bimap_rationale_additional_features">
  26 <div class="titlepage"><div><div><h3 class="title">
  27 <a name="boost_bimap.rationale.additional_features"></a><a class="link" href="additional_features.html" title="Additional Features">Additional
  28       Features</a>
  29 </h3></div></div></div>
  30 <h5>
  31 <a name="boost_bimap.rationale.additional_features.h0"></a>
  32         <span class="phrase"><a name="boost_bimap.rationale.additional_features.n_1__n_n__hashed_maps"></a></span><a class="link" href="additional_features.html#boost_bimap.rationale.additional_features.n_1__n_n__hashed_maps">N-1,
  33         N-N, hashed maps</a>
  34       </h5>
  35 <p>
  36         This is a very interesting point of the design. The framework introduced
  37         in <span class="emphasis"><em>std::set theory</em></span> permits the management of the different
  38         constraints with a very simple and conceptual approach. It is easy both to
  39         remember and to learn. The idea here is to allow the user to specify the
  40         collection type of each key directly. In order to implement this feature,
  41         we have to solve two problems:
  42       </p>
  43 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
  44 <li class="listitem">
  45             The index types of the <code class="computeroutput"><span class="identifier">multi_index_container</span></code>
  46             core now depends on the collection type used for each key.
  47           </li>
  48 <li class="listitem">
  49             The map views now change their semantics according to the collection
  50             type chosen.
  51           </li>
  52 </ul></div>
  53 <p>
  54         Boost.Bimap relies heavily on Boost.MPL to implement all of the metaprogramming
  55         necessary to make this framework work. By default, if the user does not specify
  56         the kind of the set, a <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">set</span></code> type
  57         is used.
  58       </p>
  59 <p>
  60         <span class="inlinemediaobject"><img src="../../images/bimap/bimap.structures.png" alt="bimap.structures"></span>
  61       </p>
  62 <h5>
  63 <a name="boost_bimap.rationale.additional_features.h1"></a>
  64         <span class="phrase"><a name="boost_bimap.rationale.additional_features.collection_type_of_relation_constraints"></a></span><a class="link" href="additional_features.html#boost_bimap.rationale.additional_features.collection_type_of_relation_constraints">Collection
  65         type of relation constraints</a>
  66       </h5>
  67 <p>
  68         The constraints of the bimap set view are another very important feature.
  69         In general, Boost.Bimap users will base the set view type on one of the two
  70         collection types of their keys. It may be useful however to give this set
  71         other constraints or simply to order it differently. By default, Boost.Bimap
  72         bases the collection type of relations on the left collection type, but the
  73         user may choose between:
  74       </p>
  75 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
  76 <li class="listitem">
  77             left_based
  78           </li>
  79 <li class="listitem">
  80             right_based
  81           </li>
  82 <li class="listitem">
  83             set_of_relation&lt;&gt;
  84           </li>
  85 <li class="listitem">
  86             multiset_of_relation&lt;&gt;
  87           </li>
  88 <li class="listitem">
  89             unordered_set_of_relation&lt;&gt;
  90           </li>
  91 <li class="listitem">
  92             unordered_multiset_of_relation&lt;&gt;
  93           </li>
  94 <li class="listitem">
  95             list_of
  96           </li>
  97 <li class="listitem">
  98             vector_of
  99           </li>
 100 </ul></div>
 101 <p>
 102         In the first two cases, there are only two indices in the <code class="computeroutput"><span class="identifier">multi_index_core</span></code>,
 103         and for this reason, these are the preferred options. The implementation
 104         uses further metaprogramming to define a new index if necessary.
 105       </p>
 106 <h5>
 107 <a name="boost_bimap.rationale.additional_features.h2"></a>
 108         <span class="phrase"><a name="boost_bimap.rationale.additional_features.tagged"></a></span><a class="link" href="additional_features.html#boost_bimap.rationale.additional_features.tagged">Tagged</a>
 109       </h5>
 110 <p>
 111         The idea of using tags instead of the <code class="literal">member_at::side</code>
 112         idiom is very appealing since code that uses it is more readable. The only
 113         cost is compile time. <span class="emphasis"><em>boost/bimap/tagged</em></span> is the implementation
 114         of a non-invasive tagged idiom. The <code class="literal">relation</code> class is
 115         built in such a way that even when the user uses tags, the <code class="literal">member_at::side</code>
 116         idiom continues to work. This is good since an user can start tagging even
 117         before completing the coding of the algorithm, and the untagged code continues
 118         to work. The development becomes a little more complicated when user-defined
 119         tags are included, but there are many handy metafunctions defined in the
 120         <code class="literal">tagged</code> idiom that help to keep things simple enough.
 121       </p>
 122 <p>
 123         <span class="inlinemediaobject"><img src="../../images/bimap/tagged.png" alt="tagged"></span>
 124       </p>
 125 </div>
 126 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 127 <td align="left"></td>
 128 <td align="right"><div class="copyright-footer">Copyright &#169; 2006-2012 Matias Capeletto<p>
 129         Distributed under the Boost Software License, Version 1.0. (See accompanying
 130         file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
 131       </p>
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