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| <div class="titlepage"><div><div><h2 class="title" style="clear: both"> |
| <a name="range.introduction"></a><a class="link" href="introduction.html" title="Introduction">Introduction</a> |
| </h2></div></div></div> |
| <p> |
| Generic algorithms have so far been specified in terms of two or more iterators. |
| Two iterators would together form a range of values that the algorithm could |
| work on. This leads to a very general interface, but also to a somewhat clumsy |
| use of the algorithms with redundant specification of container names. Therefore |
| we would like to raise the abstraction level for algorithms so they specify |
| their interface in terms of <a class="link" href="concepts.html" title="Range Concepts">Ranges</a> as |
| much as possible. |
| </p> |
| <p> |
| The most common form of ranges used throughout the C++ community are standard |
| library containers. When writing algorithms however, one often finds it desirable |
| for the algorithm to accept other types that offer enough functionality to |
| satisfy the needs of the generic code <span class="bold"><strong><span class="emphasis"><em>if a |
| suitable layer of indirection is applied</em></span></strong></span> . For example, |
| raw arrays are often suitable for use with generic code that works with containers, |
| provided a suitable adapter is used. Likewise, null terminated strings can |
| be treated as containers of characters, if suitably adapted. |
| </p> |
| <p> |
| This library therefore provides the means to adapt standard-like containers, |
| null terminated strings, <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">pairs</span></code> of |
| iterators, and raw arrays (and more), such that the same generic code can work |
| with them all. The basic idea is to add another layer of indirection using |
| <a href="../../../../../libs/mpl/doc/refmanual/metafunction.html" target="_top">metafunctions</a> |
| and free-standing functions so syntactic and/or semantic differences can be |
| removed. |
| </p> |
| <p> |
| The main advantages are |
| </p> |
| <div class="itemizedlist"><ul class="itemizedlist" type="disc"> |
| <li class="listitem"> |
| simpler implementation and specification of generic range algorithms |
| </li> |
| <li class="listitem"> |
| more flexible, compact and maintainable client code |
| </li> |
| <li class="listitem"> |
| safe use of built-in arrays (for legacy code; why else would you use built-in |
| arrays?) |
| </li> |
| </ul></div> |
| <a name="range.introduction.example___iterate_over_the_values_in_a_map"></a><h4> |
| <a name="id759844"></a> |
| <a class="link" href="introduction.html#range.introduction.example___iterate_over_the_values_in_a_map">Example |
| - Iterate over the values in a map</a> |
| </h4> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">;</span> |
| <span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">adaptors</span><span class="special">;</span> |
| <span class="identifier">for_each</span><span class="special">(</span> <span class="identifier">my_map</span> <span class="special">|</span> <span class="identifier">map_values</span><span class="special">,</span> <span class="identifier">fn</span> <span class="special">);</span> |
| </pre> |
| <p> |
| </p> |
| <a name="range.introduction.example___iterate_over_the_keys_in_a_map"></a><h4> |
| <a name="id759955"></a> |
| <a class="link" href="introduction.html#range.introduction.example___iterate_over_the_keys_in_a_map">Example |
| - Iterate over the keys in a map</a> |
| </h4> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">;</span> |
| <span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">adaptors</span><span class="special">;</span> |
| <span class="identifier">for_each</span><span class="special">(</span> <span class="identifier">my_map</span> <span class="special">|</span> <span class="identifier">map_keys</span><span class="special">,</span> <span class="identifier">fn</span> <span class="special">);</span> |
| </pre> |
| <p> |
| </p> |
| <a name="range.introduction.example___push_the_even_values_from_a_map_in_reverse_order_into_the_container__code__phrase_role__identifier__target__phrase___code_"></a><h4> |
| <a name="id760072"></a> |
| <a class="link" href="introduction.html#range.introduction.example___push_the_even_values_from_a_map_in_reverse_order_into_the_container__code__phrase_role__identifier__target__phrase___code_">Example |
| - Push the even values from a map in reverse order into the container <code class="computeroutput"><span class="identifier">target</span></code></a> |
| </h4> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">;</span> |
| <span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">adaptors</span><span class="special">;</span> |
| <span class="comment">// Assume that is_even is a predicate that has been implemented elsewhere... |
| </span><span class="identifier">push_back</span><span class="special">(</span><span class="identifier">target</span><span class="special">,</span> <span class="identifier">my_map</span> <span class="special">|</span> <span class="identifier">map_values</span> <span class="special">|</span> <span class="identifier">filtered</span><span class="special">(</span><span class="identifier">is_even</span><span class="special">())</span> <span class="special">|</span> <span class="identifier">reversed</span><span class="special">);</span> |
| </pre> |
| <p> |
| </p> |
| </div> |
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| <td align="left"></td> |
| <td align="right"><div class="copyright-footer">Copyright © 2003 -2010 Thorsten Ottosen, Neil Groves<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>) |
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