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<div class="section">
<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="id2984506"></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="id2984631"></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="id2982448"></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>
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