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Boost.RangeEx merged into Boost.Range [SVN r60897]
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<div class="section" title="Introduction">
<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 we are used to work with is standard library
containers. However, one often finds it desirable to extend that code to work
with 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>
<p>
Below are given a small example (the complete example can be found <a href="http://www.boost.org/libs/range/test/algorithm_example.cpp" target="_top">here</a>
):
</p>
<p>
</p>
<pre class="programlisting"><span class="comment">//
</span><span class="comment">// example: extracting bounds in a generic algorithm
</span><span class="comment">//
</span><span class="keyword">template</span><span class="special">&lt;</span> <span class="keyword">class</span> <span class="identifier">ForwardReadableRange</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">T</span> <span class="special">&gt;</span>
<span class="keyword">inline</span> <span class="keyword">typename</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">range_iterator</span><span class="special">&lt;</span> <span class="identifier">ForwardReadableRange</span> <span class="special">&gt;::</span><span class="identifier">type</span>
<span class="identifier">find</span><span class="special">(</span> <span class="identifier">ForwardReadableRange</span><span class="special">&amp;</span> <span class="identifier">c</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">T</span><span class="special">&amp;</span> <span class="identifier">value</span> <span class="special">)</span>
<span class="special">{</span>
<span class="keyword">return</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">find</span><span class="special">(</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">begin</span><span class="special">(</span> <span class="identifier">c</span> <span class="special">),</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">end</span><span class="special">(</span> <span class="identifier">c</span> <span class="special">),</span> <span class="identifier">value</span> <span class="special">);</span>
<span class="special">}</span>
<span class="keyword">template</span><span class="special">&lt;</span> <span class="keyword">class</span> <span class="identifier">ForwardReadableRange</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">T</span> <span class="special">&gt;</span>
<span class="keyword">inline</span> <span class="keyword">typename</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">range_iterator</span><span class="special">&lt;</span> <span class="keyword">const</span> <span class="identifier">ForwardReadableRange</span> <span class="special">&gt;::</span><span class="identifier">type</span>
<span class="identifier">find</span><span class="special">(</span> <span class="keyword">const</span> <span class="identifier">ForwardReadableRange</span><span class="special">&amp;</span> <span class="identifier">c</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">T</span><span class="special">&amp;</span> <span class="identifier">value</span> <span class="special">)</span>
<span class="special">{</span>
<span class="keyword">return</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">find</span><span class="special">(</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">begin</span><span class="special">(</span> <span class="identifier">c</span> <span class="special">),</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">end</span><span class="special">(</span> <span class="identifier">c</span> <span class="special">),</span> <span class="identifier">value</span> <span class="special">);</span>
<span class="special">}</span>
<span class="comment">//
</span><span class="comment">// replace first value and return its index
</span><span class="comment">//
</span><span class="keyword">template</span><span class="special">&lt;</span> <span class="keyword">class</span> <span class="identifier">ForwardReadableWriteableRange</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">T</span> <span class="special">&gt;</span>
<span class="keyword">inline</span> <span class="keyword">typename</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">range_size</span><span class="special">&lt;</span> <span class="identifier">ForwardReadableWriteableRange</span> <span class="special">&gt;::</span><span class="identifier">type</span>
<span class="identifier">my_generic_replace</span><span class="special">(</span> <span class="identifier">ForwardReadableWriteableRange</span><span class="special">&amp;</span> <span class="identifier">c</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">T</span><span class="special">&amp;</span> <span class="identifier">value</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">T</span><span class="special">&amp;</span> <span class="identifier">replacement</span> <span class="special">)</span>
<span class="special">{</span>
<span class="keyword">typename</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">range_iterator</span><span class="special">&lt;</span> <span class="identifier">ForwardReadableWriteableRange</span> <span class="special">&gt;::</span><span class="identifier">type</span> <span class="identifier">found</span> <span class="special">=</span> <span class="identifier">find</span><span class="special">(</span> <span class="identifier">c</span><span class="special">,</span> <span class="identifier">value</span> <span class="special">);</span>
<span class="keyword">if</span><span class="special">(</span> <span class="identifier">found</span> <span class="special">!=</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">end</span><span class="special">(</span> <span class="identifier">c</span> <span class="special">)</span> <span class="special">)</span>
<span class="special">*</span><span class="identifier">found</span> <span class="special">=</span> <span class="identifier">replacement</span><span class="special">;</span>
<span class="keyword">return</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">distance</span><span class="special">(</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">begin</span><span class="special">(</span> <span class="identifier">c</span> <span class="special">),</span> <span class="identifier">found</span> <span class="special">);</span>
<span class="special">}</span>
<span class="comment">//
</span><span class="comment">// usage
</span><span class="comment">//
</span><span class="keyword">const</span> <span class="keyword">int</span> <span class="identifier">N</span> <span class="special">=</span> <span class="number">5</span><span class="special">;</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;</span> <span class="identifier">my_vector</span><span class="special">;</span>
<span class="keyword">int</span> <span class="identifier">values</span><span class="special">[]</span> <span class="special">=</span> <span class="special">{</span> <span class="number">1</span><span class="special">,</span><span class="number">2</span><span class="special">,</span><span class="number">3</span><span class="special">,</span><span class="number">4</span><span class="special">,</span><span class="number">5</span><span class="special">,</span><span class="number">6</span><span class="special">,</span><span class="number">7</span><span class="special">,</span><span class="number">8</span><span class="special">,</span><span class="number">9</span> <span class="special">};</span>
<span class="identifier">my_vector</span><span class="special">.</span><span class="identifier">assign</span><span class="special">(</span> <span class="identifier">values</span><span class="special">,</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">end</span><span class="special">(</span> <span class="identifier">values</span> <span class="special">)</span> <span class="special">);</span>
<span class="keyword">typedef</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;::</span><span class="identifier">iterator</span> <span class="identifier">iterator</span><span class="special">;</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span><span class="special">&lt;</span><span class="identifier">iterator</span><span class="special">,</span><span class="identifier">iterator</span><span class="special">&gt;</span> <span class="identifier">my_view</span><span class="special">(</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">begin</span><span class="special">(</span> <span class="identifier">my_vector</span> <span class="special">),</span>
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">begin</span><span class="special">(</span> <span class="identifier">my_vector</span> <span class="special">)</span> <span class="special">+</span> <span class="identifier">N</span> <span class="special">);</span>
<span class="keyword">char</span> <span class="identifier">str_val</span><span class="special">[]</span> <span class="special">=</span> <span class="string">"a string"</span><span class="special">;</span>
<span class="keyword">char</span><span class="special">*</span> <span class="identifier">str</span> <span class="special">=</span> <span class="identifier">str_val</span><span class="special">;</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="identifier">my_generic_replace</span><span class="special">(</span> <span class="identifier">my_vector</span><span class="special">,</span> <span class="number">4</span><span class="special">,</span> <span class="number">2</span> <span class="special">);</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="identifier">my_generic_replace</span><span class="special">(</span> <span class="identifier">my_view</span><span class="special">,</span> <span class="number">4</span><span class="special">,</span> <span class="number">2</span> <span class="special">);</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="identifier">my_generic_replace</span><span class="special">(</span> <span class="identifier">str</span><span class="special">,</span> <span class="char">'a'</span><span class="special">,</span> <span class="char">'b'</span> <span class="special">);</span>
<span class="comment">// prints '3', '5' and '0'
</span></pre>
<p>
</p>
<p>
By using the free-standing functions and <a href="../../../libs/mpl/doc/refmanual/metafunction.html" target="_top">metafunctions</a>,
the code automatically works for all the types supported by this library; now
and in the future. Notice that we have to provide two versions of <code class="computeroutput"><span class="identifier">find</span><span class="special">()</span></code> since
we cannot forward a non-const rvalue with reference arguments (see this article
about <a href="http://std.dkuug.dk/jtc1/sc22/wg21/docs/papers/2002/n1385.htm" target="_top">The
Forwarding Problem</a> ).
</p>
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