<html> <head> <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> <title>Method 2: provide free-standing functions and specialize metafunctions</title> <link rel="stylesheet" href="../../../../../../../doc/src/boostbook.css" type="text/css"> <meta name="generator" content="DocBook XSL Stylesheets V1.75.2"> <link rel="home" href="../../../index.html" title="Chapter 1. Range 2.0"> <link rel="up" href="../extending.html" title="Extending the library"> <link rel="prev" href="method_1.html" title="Method 1: provide member functions and nested types"> <link rel="next" href="method_3.html" title="Method 3: provide range adaptor implementations"> </head> <body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> <table cellpadding="2" width="100%"><tr> <td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../../boost.png"></td> <td align="center"><a href="../../../../../../../index.html">Home</a></td> <td align="center"><a href="../../../../../../../libs/libraries.htm">Libraries</a></td> <td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> <td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> <td align="center"><a href="../../../../../../../more/index.htm">More</a></td> </tr></table> <hr> <div class="spirit-nav"> <a accesskey="p" href="method_1.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../extending.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="method_3.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a> </div> <div class="section"> <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>) </p> </div></td> </tr></table> <hr> <div class="spirit-nav"> <a accesskey="p" href="method_1.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../extending.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="method_3.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a> </div> </body> </html>