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| <div class="titlepage"><div><div><h4 class="title"> |
| <a name="range.reference.extending.method_2"></a><a class="link" href="method_2.html" title="Method 2: provide free-standing functions and specialize metafunctions"> Method 2: provide |
| free-standing functions and specialize metafunctions</a> |
| </h4></div></div></div> |
| <p> |
| This procedure assumes that you cannot (or do not wish to) change the types |
| that should be made conformant to a Range concept. If this is not true, |
| see <a class="link" href="method_1.html" title="Method 1: provide member functions and nested types">method 1</a>. |
| </p> |
| <p> |
| The primary templates in this library are implemented such that certain |
| functions are found via argument-dependent-lookup (ADL). Below is given |
| an overview of which free-standing functions a class must specify to be |
| useable as a certain Range concept. Let <code class="computeroutput"><span class="identifier">x</span></code> |
| be a variable (<code class="computeroutput"><span class="keyword">const</span></code> or <code class="computeroutput"><span class="keyword">mutable</span></code>) of the class in question. |
| </p> |
| <div class="informaltable"><table class="table"> |
| <colgroup> |
| <col> |
| <col> |
| </colgroup> |
| <thead><tr> |
| <th> |
| <p> |
| Function |
| </p> |
| </th> |
| <th> |
| <p> |
| Related concept |
| </p> |
| </th> |
| </tr></thead> |
| <tbody> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">range_begin</span><span class="special">(</span><span class="identifier">x</span><span class="special">)</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| <a class="link" href="../../concepts/single_pass_range.html" title="Single Pass Range">Single Pass |
| Range</a> |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">range_end</span><span class="special">(</span><span class="identifier">x</span><span class="special">)</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| <a class="link" href="../../concepts/single_pass_range.html" title="Single Pass Range">Single Pass |
| Range</a> |
| </p> |
| </td> |
| </tr> |
| </tbody> |
| </table></div> |
| <p> |
| <code class="computeroutput"><span class="identifier">range_begin</span><span class="special">()</span></code> |
| and <code class="computeroutput"><span class="identifier">range_end</span><span class="special">()</span></code> |
| must be overloaded for both <code class="computeroutput"><span class="keyword">const</span></code> |
| and <code class="computeroutput"><span class="keyword">mutable</span></code> reference arguments. |
| </p> |
| <p> |
| You must also specialize two metafunctions for your type <code class="computeroutput"><span class="identifier">X</span></code>: |
| </p> |
| <div class="informaltable"><table class="table"> |
| <colgroup> |
| <col> |
| <col> |
| </colgroup> |
| <thead><tr> |
| <th> |
| <p> |
| Metafunction |
| </p> |
| </th> |
| <th> |
| <p> |
| Related concept |
| </p> |
| </th> |
| </tr></thead> |
| <tbody> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">range_mutable_iterator</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| <a class="link" href="../../concepts/single_pass_range.html" title="Single Pass Range">Single Pass |
| Range</a> |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">range_const_iterator</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| <a class="link" href="../../concepts/single_pass_range.html" title="Single Pass Range">Single Pass |
| Range</a> |
| </p> |
| </td> |
| </tr> |
| </tbody> |
| </table></div> |
| <p> |
| A complete example is given here: |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">range</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> |
| <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">iterator</span><span class="special">></span> <span class="comment">// for std::iterator_traits, std::distance() |
| </span> |
| <span class="keyword">namespace</span> <span class="identifier">Foo</span> |
| <span class="special">{</span> |
| <span class="comment">// |
| </span> <span class="comment">// Our sample UDT. A 'Pair' |
| </span> <span class="comment">// will work as a range when the stored |
| </span> <span class="comment">// elements are iterators. |
| </span> <span class="comment">// |
| </span> <span class="keyword">template</span><span class="special"><</span> <span class="keyword">class</span> <span class="identifier">T</span> <span class="special">></span> |
| <span class="keyword">struct</span> <span class="identifier">Pair</span> |
| <span class="special">{</span> |
| <span class="identifier">T</span> <span class="identifier">first</span><span class="special">,</span> <span class="identifier">last</span><span class="special">;</span> |
| <span class="special">};</span> |
| |
| <span class="special">}</span> <span class="comment">// namespace 'Foo' |
| </span> |
| <span class="keyword">namespace</span> <span class="identifier">boost</span> |
| <span class="special">{</span> |
| <span class="comment">// |
| </span> <span class="comment">// Specialize metafunctions. We must include the range.hpp header. |
| </span> <span class="comment">// We must open the 'boost' namespace. |
| </span> <span class="comment">// |
| </span> |
| <span class="keyword">template</span><span class="special"><</span> <span class="keyword">class</span> <span class="identifier">T</span> <span class="special">></span> |
| <span class="keyword">struct</span> <span class="identifier">range_mutable_iterator</span><span class="special"><</span> <span class="identifier">Foo</span><span class="special">::</span><span class="identifier">Pair</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="special">></span> |
| <span class="special">{</span> |
| <span class="keyword">typedef</span> <span class="identifier">T</span> <span class="identifier">type</span><span class="special">;</span> |
| <span class="special">};</span> |
| |
| <span class="keyword">template</span><span class="special"><</span> <span class="keyword">class</span> <span class="identifier">T</span> <span class="special">></span> |
| <span class="keyword">struct</span> <span class="identifier">range_const_iterator</span><span class="special"><</span> <span class="identifier">Foo</span><span class="special">::</span><span class="identifier">Pair</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="special">></span> |
| <span class="special">{</span> |
| <span class="comment">// |
| </span> <span class="comment">// Remark: this is defined similar to 'range_iterator' |
| </span> <span class="comment">// because the 'Pair' type does not distinguish |
| </span> <span class="comment">// between an iterator and a const_iterator. |
| </span> <span class="comment">// |
| </span> <span class="keyword">typedef</span> <span class="identifier">T</span> <span class="identifier">type</span><span class="special">;</span> |
| <span class="special">};</span> |
| |
| <span class="special">}</span> <span class="comment">// namespace 'boost' |
| </span> |
| <span class="keyword">namespace</span> <span class="identifier">Foo</span> |
| <span class="special">{</span> |
| <span class="comment">// |
| </span> <span class="comment">// The required functions. These should be defined in |
| </span> <span class="comment">// the same namespace as 'Pair', in this case |
| </span> <span class="comment">// in namespace 'Foo'. |
| </span> <span class="comment">// |
| </span> |
| <span class="keyword">template</span><span class="special"><</span> <span class="keyword">class</span> <span class="identifier">T</span> <span class="special">></span> |
| <span class="keyword">inline</span> <span class="identifier">T</span> <span class="identifier">range_begin</span><span class="special">(</span> <span class="identifier">Pair</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&</span> <span class="identifier">x</span> <span class="special">)</span> |
| <span class="special">{</span> |
| <span class="keyword">return</span> <span class="identifier">x</span><span class="special">.</span><span class="identifier">first</span><span class="special">;</span> |
| <span class="special">}</span> |
| |
| <span class="keyword">template</span><span class="special"><</span> <span class="keyword">class</span> <span class="identifier">T</span> <span class="special">></span> |
| <span class="keyword">inline</span> <span class="identifier">T</span> <span class="identifier">range_begin</span><span class="special">(</span> <span class="keyword">const</span> <span class="identifier">Pair</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&</span> <span class="identifier">x</span> <span class="special">)</span> |
| <span class="special">{</span> |
| <span class="keyword">return</span> <span class="identifier">x</span><span class="special">.</span><span class="identifier">first</span><span class="special">;</span> |
| <span class="special">}</span> |
| |
| <span class="keyword">template</span><span class="special"><</span> <span class="keyword">class</span> <span class="identifier">T</span> <span class="special">></span> |
| <span class="keyword">inline</span> <span class="identifier">T</span> <span class="identifier">range_end</span><span class="special">(</span> <span class="identifier">Pair</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&</span> <span class="identifier">x</span> <span class="special">)</span> |
| <span class="special">{</span> |
| <span class="keyword">return</span> <span class="identifier">x</span><span class="special">.</span><span class="identifier">last</span><span class="special">;</span> |
| <span class="special">}</span> |
| |
| <span class="keyword">template</span><span class="special"><</span> <span class="keyword">class</span> <span class="identifier">T</span> <span class="special">></span> |
| <span class="keyword">inline</span> <span class="identifier">T</span> <span class="identifier">range_end</span><span class="special">(</span> <span class="keyword">const</span> <span class="identifier">Pair</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&</span> <span class="identifier">x</span> <span class="special">)</span> |
| <span class="special">{</span> |
| <span class="keyword">return</span> <span class="identifier">x</span><span class="special">.</span><span class="identifier">last</span><span class="special">;</span> |
| <span class="special">}</span> |
| |
| <span class="special">}</span> <span class="comment">// namespace 'Foo' |
| </span> |
| <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">vector</span><span class="special">></span> |
| |
| <span class="keyword">int</span> <span class="identifier">main</span><span class="special">(</span><span class="keyword">int</span> <span class="identifier">argc</span><span class="special">,</span> <span class="keyword">const</span> <span class="keyword">char</span><span class="special">*</span> <span class="identifier">argv</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"><</span><span class="keyword">int</span><span class="special">>::</span><span class="identifier">iterator</span> <span class="identifier">iter</span><span class="special">;</span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">vec</span><span class="special">;</span> |
| <span class="identifier">Foo</span><span class="special">::</span><span class="identifier">Pair</span><span class="special"><</span><span class="identifier">iter</span><span class="special">></span> <span class="identifier">pair</span> <span class="special">=</span> <span class="special">{</span> <span class="identifier">vec</span><span class="special">.</span><span class="identifier">begin</span><span class="special">(),</span> <span class="identifier">vec</span><span class="special">.</span><span class="identifier">end</span><span class="special">()</span> <span class="special">};</span> |
| <span class="keyword">const</span> <span class="identifier">Foo</span><span class="special">::</span><span class="identifier">Pair</span><span class="special"><</span><span class="identifier">iter</span><span class="special">>&</span> <span class="identifier">cpair</span> <span class="special">=</span> <span class="identifier">pair</span><span class="special">;</span> |
| <span class="comment">// |
| </span> <span class="comment">// Notice that we call 'begin' etc with qualification. |
| </span> <span class="comment">// |
| </span> <span class="identifier">iter</span> <span class="identifier">i</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">pair</span> <span class="special">);</span> |
| <span class="identifier">iter</span> <span class="identifier">e</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">pair</span> <span class="special">);</span> |
| <span class="identifier">i</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">cpair</span> <span class="special">);</span> |
| <span class="identifier">e</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">cpair</span> <span class="special">);</span> |
| <span class="identifier">boost</span><span class="special">::</span><span class="identifier">range_difference</span><span class="special"><</span> <span class="identifier">Foo</span><span class="special">::</span><span class="identifier">Pair</span><span class="special"><</span><span class="identifier">iter</span><span class="special">></span> <span class="special">>::</span><span class="identifier">type</span> <span class="identifier">s</span> <span class="special">=</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">size</span><span class="special">(</span> <span class="identifier">pair</span> <span class="special">);</span> |
| <span class="identifier">s</span> <span class="special">=</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">size</span><span class="special">(</span> <span class="identifier">cpair</span> <span class="special">);</span> |
| <span class="identifier">boost</span><span class="special">::</span><span class="identifier">range_reverse_iterator</span><span class="special"><</span> <span class="keyword">const</span> <span class="identifier">Foo</span><span class="special">::</span><span class="identifier">Pair</span><span class="special"><</span><span class="identifier">iter</span><span class="special">></span> <span class="special">>::</span><span class="identifier">type</span> |
| <span class="identifier">ri</span> <span class="special">=</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">rbegin</span><span class="special">(</span> <span class="identifier">cpair</span> <span class="special">),</span> |
| <span class="identifier">re</span> <span class="special">=</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">rend</span><span class="special">(</span> <span class="identifier">cpair</span> <span class="special">);</span> |
| |
| <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> |
| <span class="special">}</span> |
| </pre> |
| <p> |
| </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 © 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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