boost_1_45_0/libs/iterator/doc/pointee.html - nest-learning-thermostat/5.0/boost - Git at Google

 <?xml version="1.0" encoding="utf-8" ?>
 <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
 <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
 <head>
 <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
 <meta name="generator" content="Docutils 0.5: http://docutils.sourceforge.net/" />
 <title>pointee and indirect_reference</title>
 <meta name="author" content="David Abrahams" />
 <meta name="organization" content="Boost Consulting" />
 <meta name="date" content="2006-09-11" />
 <meta name="copyright" content="Copyright David Abrahams 2004." />
 <link rel="stylesheet" href="../../../rst.css" type="text/css" />
 </head>
 <body>
 <div class="document" id="pointee-and-indirect-reference">
 <h1 class="title"><tt class="docutils literal"><span class="pre">pointee</span></tt> and <tt class="docutils literal"><span class="pre">indirect_reference</span></tt></h1>
 <table class="docinfo" frame="void" rules="none">
 <col class="docinfo-name" />
 <col class="docinfo-content" />
 <tbody valign="top">
 <tr><th class="docinfo-name">Author:</th>
 <td>David Abrahams</td></tr>
 <tr><th class="docinfo-name">Contact:</th>
 <td><a class="first last reference external" href="mailto:dave&#64;boost-consulting.com">dave&#64;boost-consulting.com</a></td></tr>
 <tr><th class="docinfo-name">Organization:</th>
 <td><a class="first last reference external" href="http://www.boost-consulting.com">Boost Consulting</a></td></tr>
 <tr><th class="docinfo-name">Date:</th>
 <td>2006-09-11</td></tr>
 <tr><th class="docinfo-name">Copyright:</th>
 <td>Copyright David Abrahams 2004.</td></tr>
 </tbody>
 </table>
 <!-- Distributed under the Boost -->
 <!-- Software License, Version 1.0. (See accompanying -->
 <!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) -->
 <table class="docutils field-list" frame="void" rules="none">
 <col class="field-name" />
 <col class="field-body" />
 <tbody valign="top">
 <tr class="field"><th class="field-name">abstract:</th><td class="field-body">Provides the capability to deduce the referent types of
 pointers, smart pointers and iterators in generic code.</td>
 </tr>
 </tbody>
 </table>
 <div class="section" id="overview">
 <h1>Overview</h1>
 <p>Have you ever wanted to write a generic function that can operate
 on any kind of dereferenceable object?  If you have, you've
 probably run into the problem of how to determine the type that the
 object &quot;points at&quot;:</p>
 <pre class="literal-block">
 template &lt;class Dereferenceable&gt;
 void f(Dereferenceable p)
 {
     <em>what-goes-here?</em> value = *p;
     ...
 }
 </pre>
 <div class="section" id="pointee">
 <h2><tt class="docutils literal"><span class="pre">pointee</span></tt></h2>
 <p>It turns out to be impossible to come up with a fully-general
 algorithm to do determine <em>what-goes-here</em> directly, but it is
 possible to require that <tt class="docutils literal"><span class="pre">pointee&lt;Dereferenceable&gt;::type</span></tt> is
 correct. Naturally, <tt class="docutils literal"><span class="pre">pointee</span></tt> has the same difficulty: it can't
 determine the appropriate <tt class="docutils literal"><span class="pre">::type</span></tt> reliably for all
 <tt class="docutils literal"><span class="pre">Dereferenceable</span></tt>s, but it makes very good guesses (it works
 for all pointers, standard and boost smart pointers, and
 iterators), and when it guesses wrongly, it can be specialized as
 necessary:</p>
 <pre class="literal-block">
 namespace boost
 {
   template &lt;class T&gt;
   struct pointee&lt;third_party_lib::smart_pointer&lt;T&gt; &gt;
   {
       typedef T type;
   };
 }
 </pre>
 </div>
 <div class="section" id="indirect-reference">
 <h2><tt class="docutils literal"><span class="pre">indirect_reference</span></tt></h2>
 <p><tt class="docutils literal"><span class="pre">indirect_reference&lt;T&gt;::type</span></tt> is rather more specialized than
 <tt class="docutils literal"><span class="pre">pointee</span></tt>, and is meant to be used to forward the result of
 dereferencing an object of its argument type.  Most dereferenceable
 types just return a reference to their pointee, but some return
 proxy references or return the pointee by value.  When that
 information is needed, call on <tt class="docutils literal"><span class="pre">indirect_reference</span></tt>.</p>
 <p>Both of these templates are essential to the correct functioning of
 <a class="reference external" href="indirect_iterator.html"><tt class="docutils literal"><span class="pre">indirect_iterator</span></tt></a>.</p>
 </div>
 </div>
 <div class="section" id="reference">
 <h1>Reference</h1>
 <div class="section" id="id1">
 <h2><tt class="docutils literal"><span class="pre">pointee</span></tt></h2>
 <!-- Copyright David Abrahams 2004. Use, modification and distribution is -->
 <!-- subject to the Boost Software License, Version 1.0. (See accompanying -->
 <!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) -->
 <pre class="literal-block">
 template &lt;class Dereferenceable&gt;
 struct pointee
 {
     typedef /* see below */ type;
 };
 </pre>
 <table class="docutils field-list" frame="void" rules="none">
 <col class="field-name" />
 <col class="field-body" />
 <tbody valign="top">
 <tr class="field"><th class="field-name">Requires:</th><td class="field-body">For an object <tt class="docutils literal"><span class="pre">x</span></tt> of type <tt class="docutils literal"><span class="pre">Dereferenceable</span></tt>, <tt class="docutils literal"><span class="pre">*x</span></tt>
 is well-formed.  If <tt class="docutils literal"><span class="pre">++x</span></tt> is ill-formed it shall neither be
 ambiguous nor shall it violate access control, and
 <tt class="docutils literal"><span class="pre">Dereferenceable::element_type</span></tt> shall be an accessible type.
 Otherwise <tt class="docutils literal"><span class="pre">iterator_traits&lt;Dereferenceable&gt;::value_type</span></tt> shall
 be well formed.  [Note: These requirements need not apply to
 explicit or partial specializations of <tt class="docutils literal"><span class="pre">pointee</span></tt>]</td>
 </tr>
 </tbody>
 </table>
 <p><tt class="docutils literal"><span class="pre">type</span></tt> is determined according to the following algorithm, where
 <tt class="docutils literal"><span class="pre">x</span></tt> is an object of type <tt class="docutils literal"><span class="pre">Dereferenceable</span></tt>:</p>
 <pre class="literal-block">
 if ( ++x is ill-formed )
 {
     return ``Dereferenceable::element_type``
 }
 else if (``*x`` is a mutable reference to
          std::iterator_traits&lt;Dereferenceable&gt;::value_type)
 {
     return iterator_traits&lt;Dereferenceable&gt;::value_type
 }
 else
 {
     return iterator_traits&lt;Dereferenceable&gt;::value_type const
 }
 </pre>
 </div>
 <div class="section" id="id2">
 <h2><tt class="docutils literal"><span class="pre">indirect_reference</span></tt></h2>
 <!-- Copyright David Abrahams 2004. Use, modification and distribution is -->
 <!-- subject to the Boost Software License, Version 1.0. (See accompanying -->
 <!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) -->
 <pre class="literal-block">
 template &lt;class Dereferenceable&gt;
 struct indirect_reference
 {
     typedef /* see below */ type;
 };
 </pre>
 <table class="docutils field-list" frame="void" rules="none">
 <col class="field-name" />
 <col class="field-body" />
 <tbody valign="top">
 <tr class="field"><th class="field-name">Requires:</th><td class="field-body">For an object <tt class="docutils literal"><span class="pre">x</span></tt> of type <tt class="docutils literal"><span class="pre">Dereferenceable</span></tt>, <tt class="docutils literal"><span class="pre">*x</span></tt>
 is well-formed.  If <tt class="docutils literal"><span class="pre">++x</span></tt> is ill-formed it shall neither be
 ambiguous nor shall it violate access control, and
 <tt class="docutils literal"><span class="pre">pointee&lt;Dereferenceable&gt;::type&amp;</span></tt> shall be well-formed.
 Otherwise <tt class="docutils literal"><span class="pre">iterator_traits&lt;Dereferenceable&gt;::reference</span></tt> shall
 be well formed.  [Note: These requirements need not apply to
 explicit or partial specializations of <tt class="docutils literal"><span class="pre">indirect_reference</span></tt>]</td>
 </tr>
 </tbody>
 </table>
 <p><tt class="docutils literal"><span class="pre">type</span></tt> is determined according to the following algorithm, where
 <tt class="docutils literal"><span class="pre">x</span></tt> is an object of type <tt class="docutils literal"><span class="pre">Dereferenceable</span></tt>:</p>
 <pre class="literal-block">
 if ( ++x is ill-formed )
     return ``pointee&lt;Dereferenceable&gt;::type&amp;``
 else
     std::iterator_traits&lt;Dereferenceable&gt;::reference
 </pre>
 </div>
 </div>
 </div>
 <div class="footer">
 <hr class="footer" />
 <a class="reference external" href="pointee.rst">View document source</a>.
 Generated by <a class="reference external" href="http://docutils.sourceforge.net/">Docutils</a> from <a class="reference external" href="http://docutils.sourceforge.net/rst.html">reStructuredText</a> source.

 </div>
 </body>
 </html>
	<?xml version="1.0" encoding="utf-8" ?>
	<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
	<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
	<head>
	<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
	<meta name="generator" content="Docutils 0.5: http://docutils.sourceforge.net/" />
	<title>pointee and indirect_reference</title>
	<meta name="author" content="David Abrahams" />
	<meta name="organization" content="Boost Consulting" />
	<meta name="date" content="2006-09-11" />
	<meta name="copyright" content="Copyright David Abrahams 2004." />
	<link rel="stylesheet" href="../../../rst.css" type="text/css" />
	</head>
	<body>
	<div class="document" id="pointee-and-indirect-reference">
	<h1 class="title"><tt class="docutils literal"><span class="pre">pointee</span></tt> and <tt class="docutils literal"><span class="pre">indirect_reference</span></tt></h1>
	<table class="docinfo" frame="void" rules="none">
	<col class="docinfo-name" />
	<col class="docinfo-content" />
	<tbody valign="top">
	<tr><th class="docinfo-name">Author:</th>
	<td>David Abrahams</td></tr>
	<tr><th class="docinfo-name">Contact:</th>
	<td><a class="first last reference external" href="mailto:dave@boost-consulting.com">dave@boost-consulting.com</a></td></tr>
	<tr><th class="docinfo-name">Organization:</th>
	<td><a class="first last reference external" href="http://www.boost-consulting.com">Boost Consulting</a></td></tr>
	<tr><th class="docinfo-name">Date:</th>
	<td>2006-09-11</td></tr>
	<tr><th class="docinfo-name">Copyright:</th>
	<td>Copyright David Abrahams 2004.</td></tr>
	</tbody>
	</table>
	<!-- Distributed under the Boost -->
	<!-- Software License, Version 1.0. (See accompanying -->
	<!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) -->
	<table class="docutils field-list" frame="void" rules="none">
	<col class="field-name" />
	<col class="field-body" />
	<tbody valign="top">
	<tr class="field"><th class="field-name">abstract:</th><td class="field-body">Provides the capability to deduce the referent types of
	pointers, smart pointers and iterators in generic code.</td>
	</tr>
	</tbody>
	</table>
	<div class="section" id="overview">
	<h1>Overview</h1>
	<p>Have you ever wanted to write a generic function that can operate
	on any kind of dereferenceable object? If you have, you've
	probably run into the problem of how to determine the type that the
	object "points at":</p>
	<pre class="literal-block">
	template <class Dereferenceable>
	void f(Dereferenceable p)
	{
	<em>what-goes-here?</em> value = *p;
	...
	}
	</pre>
	<div class="section" id="pointee">
	<h2><tt class="docutils literal"><span class="pre">pointee</span></tt></h2>
	<p>It turns out to be impossible to come up with a fully-general
	algorithm to do determine <em>what-goes-here</em> directly, but it is
	possible to require that <tt class="docutils literal"><span class="pre">pointee<Dereferenceable>::type</span></tt> is
	correct. Naturally, <tt class="docutils literal"><span class="pre">pointee</span></tt> has the same difficulty: it can't
	determine the appropriate <tt class="docutils literal"><span class="pre">::type</span></tt> reliably for all
	<tt class="docutils literal"><span class="pre">Dereferenceable</span></tt>s, but it makes very good guesses (it works
	for all pointers, standard and boost smart pointers, and
	iterators), and when it guesses wrongly, it can be specialized as
	necessary:</p>
	<pre class="literal-block">
	namespace boost
	{
	template <class T>
	struct pointee<third_party_lib::smart_pointer<T> >
	{
	typedef T type;
	};
	}
	</pre>
	</div>
	<div class="section" id="indirect-reference">
	<h2><tt class="docutils literal"><span class="pre">indirect_reference</span></tt></h2>
	<p><tt class="docutils literal"><span class="pre">indirect_reference<T>::type</span></tt> is rather more specialized than
	<tt class="docutils literal"><span class="pre">pointee</span></tt>, and is meant to be used to forward the result of
	dereferencing an object of its argument type. Most dereferenceable
	types just return a reference to their pointee, but some return
	proxy references or return the pointee by value. When that
	information is needed, call on <tt class="docutils literal"><span class="pre">indirect_reference</span></tt>.</p>
	<p>Both of these templates are essential to the correct functioning of
	<a class="reference external" href="indirect_iterator.html"><tt class="docutils literal"><span class="pre">indirect_iterator</span></tt></a>.</p>
	</div>
	</div>
	<div class="section" id="reference">
	<h1>Reference</h1>
	<div class="section" id="id1">
	<h2><tt class="docutils literal"><span class="pre">pointee</span></tt></h2>
	<!-- Copyright David Abrahams 2004. Use, modification and distribution is -->
	<!-- subject to the Boost Software License, Version 1.0. (See accompanying -->
	<!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) -->
	<pre class="literal-block">
	template <class Dereferenceable>
	struct pointee
	{
	typedef /* see below */ type;
	};
	</pre>
	<table class="docutils field-list" frame="void" rules="none">
	<col class="field-name" />
	<col class="field-body" />
	<tbody valign="top">
	<tr class="field"><th class="field-name">Requires:</th><td class="field-body">For an object <tt class="docutils literal"><span class="pre">x</span></tt> of type <tt class="docutils literal"><span class="pre">Dereferenceable</span></tt>, <tt class="docutils literal"><span class="pre">*x</span></tt>
	is well-formed. If <tt class="docutils literal"><span class="pre">++x</span></tt> is ill-formed it shall neither be
	ambiguous nor shall it violate access control, and
	<tt class="docutils literal"><span class="pre">Dereferenceable::element_type</span></tt> shall be an accessible type.
	Otherwise <tt class="docutils literal"><span class="pre">iterator_traits<Dereferenceable>::value_type</span></tt> shall
	be well formed. [Note: These requirements need not apply to
	explicit or partial specializations of <tt class="docutils literal"><span class="pre">pointee</span></tt>]</td>
	</tr>
	</tbody>
	</table>
	<p><tt class="docutils literal"><span class="pre">type</span></tt> is determined according to the following algorithm, where
	<tt class="docutils literal"><span class="pre">x</span></tt> is an object of type <tt class="docutils literal"><span class="pre">Dereferenceable</span></tt>:</p>
	<pre class="literal-block">
	if ( ++x is ill-formed )
	{
	return ``Dereferenceable::element_type``
	}
	else if (``*x`` is a mutable reference to
	std::iterator_traits<Dereferenceable>::value_type)
	{
	return iterator_traits<Dereferenceable>::value_type
	}
	else
	{
	return iterator_traits<Dereferenceable>::value_type const
	}
	</pre>
	</div>
	<div class="section" id="id2">
	<h2><tt class="docutils literal"><span class="pre">indirect_reference</span></tt></h2>
	<!-- Copyright David Abrahams 2004. Use, modification and distribution is -->
	<!-- subject to the Boost Software License, Version 1.0. (See accompanying -->
	<!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) -->
	<pre class="literal-block">
	template <class Dereferenceable>
	struct indirect_reference
	{
	typedef /* see below */ type;
	};
	</pre>
	<table class="docutils field-list" frame="void" rules="none">
	<col class="field-name" />
	<col class="field-body" />
	<tbody valign="top">
	<tr class="field"><th class="field-name">Requires:</th><td class="field-body">For an object <tt class="docutils literal"><span class="pre">x</span></tt> of type <tt class="docutils literal"><span class="pre">Dereferenceable</span></tt>, <tt class="docutils literal"><span class="pre">*x</span></tt>
	is well-formed. If <tt class="docutils literal"><span class="pre">++x</span></tt> is ill-formed it shall neither be
	ambiguous nor shall it violate access control, and
	<tt class="docutils literal"><span class="pre">pointee<Dereferenceable>::type&</span></tt> shall be well-formed.
	Otherwise <tt class="docutils literal"><span class="pre">iterator_traits<Dereferenceable>::reference</span></tt> shall
	be well formed. [Note: These requirements need not apply to
	explicit or partial specializations of <tt class="docutils literal"><span class="pre">indirect_reference</span></tt>]</td>
	</tr>
	</tbody>
	</table>
	<p><tt class="docutils literal"><span class="pre">type</span></tt> is determined according to the following algorithm, where
	<tt class="docutils literal"><span class="pre">x</span></tt> is an object of type <tt class="docutils literal"><span class="pre">Dereferenceable</span></tt>:</p>
	<pre class="literal-block">
	if ( ++x is ill-formed )
	return ``pointee<Dereferenceable>::type&``
	else
	std::iterator_traits<Dereferenceable>::reference
	</pre>
	</div>
	</div>
	</div>
	<div class="footer">
	<hr class="footer" />
	<a class="reference external" href="pointee.rst">View document source</a>.
	Generated by <a class="reference external" href="http://docutils.sourceforge.net/">Docutils</a> from <a class="reference external" href="http://docutils.sourceforge.net/rst.html">reStructuredText</a> source.

	</div>
	</body>
	</html>