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- <div class="titlepage"><div><div><h3 class="title">
- <a name="boost_bimap.rationale.additional_features"></a><a class="link" href="additional_features.html" title="Additional Features">Additional
- Features</a>
- </h3></div></div></div>
- <h5>
- <a name="boost_bimap.rationale.additional_features.h0"></a>
- <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,
- N-N, hashed maps</a>
- </h5>
- <p>
- This is a very interesting point of the design. The framework introduced
- in <span class="emphasis"><em>std::set theory</em></span> permits the management of the different
- constraints with a very simple and conceptual approach. It is easy both to
- remember and to learn. The idea here is to allow the user to specify the
- collection type of each key directly. In order to implement this feature,
- we have to solve two problems:
- </p>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
- <li class="listitem">
- The index types of the <code class="computeroutput"><span class="identifier">multi_index_container</span></code>
- core now depends on the collection type used for each key.
- </li>
- <li class="listitem">
- The map views now change their semantics according to the collection
- type chosen.
- </li>
- </ul></div>
- <p>
- Boost.Bimap relies heavily on Boost.MPL to implement all of the metaprogramming
- necessary to make this framework work. By default, if the user does not specify
- 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
- is used.
- </p>
- <p>
- <span class="inlinemediaobject"><img src="../../images/bimap/bimap.structures.png" alt="bimap.structures"></span>
- </p>
- <h5>
- <a name="boost_bimap.rationale.additional_features.h1"></a>
- <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
- type of relation constraints</a>
- </h5>
- <p>
- The constraints of the bimap set view are another very important feature.
- In general, Boost.Bimap users will base the set view type on one of the two
- collection types of their keys. It may be useful however to give this set
- other constraints or simply to order it differently. By default, Boost.Bimap
- bases the collection type of relations on the left collection type, but the
- user may choose between:
- </p>
- <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
- <li class="listitem">
- left_based
- </li>
- <li class="listitem">
- right_based
- </li>
- <li class="listitem">
- set_of_relation<>
- </li>
- <li class="listitem">
- multiset_of_relation<>
- </li>
- <li class="listitem">
- unordered_set_of_relation<>
- </li>
- <li class="listitem">
- unordered_multiset_of_relation<>
- </li>
- <li class="listitem">
- list_of
- </li>
- <li class="listitem">
- vector_of
- </li>
- </ul></div>
- <p>
- In the first two cases, there are only two indices in the <code class="computeroutput"><span class="identifier">multi_index_core</span></code>,
- and for this reason, these are the preferred options. The implementation
- uses further metaprogramming to define a new index if necessary.
- </p>
- <h5>
- <a name="boost_bimap.rationale.additional_features.h2"></a>
- <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>
- </h5>
- <p>
- The idea of using tags instead of the <code class="literal">member_at::side</code>
- idiom is very appealing since code that uses it is more readable. The only
- cost is compile time. <span class="emphasis"><em>boost/bimap/tagged</em></span> is the implementation
- of a non-invasive tagged idiom. The <code class="literal">relation</code> class is
- built in such a way that even when the user uses tags, the <code class="literal">member_at::side</code>
- idiom continues to work. This is good since an user can start tagging even
- before completing the coding of the algorithm, and the untagged code continues
- to work. The development becomes a little more complicated when user-defined
- tags are included, but there are many handy metafunctions defined in the
- <code class="literal">tagged</code> idiom that help to keep things simple enough.
- </p>
- <p>
- <span class="inlinemediaobject"><img src="../../images/bimap/tagged.png" alt="tagged"></span>
- </p>
- </div>
- <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
- <td align="left"></td>
- <td align="right"><div class="copyright-footer">Copyright © 2006-2012 Matias Capeletto<p>
- Distributed under the Boost Software License, Version 1.0. (See accompanying
- 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>)
- </p>
- </div></td>
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