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added make_xxx functions for some of the iterators

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[SVN r21611]
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Jeremy Siek
2004-01-12 01:30:47 +00:00
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@ -3,204 +3,13 @@
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<title>Iterator Facade</title>
<meta name="author" content="David Abrahams, Jeremy Siek, Thomas Witt" />
<meta name="organization" content="Boost Consulting, Indiana University Open Systems Lab, University of Hanover Institute for Transport Railway Operation and Construction" />
<meta name="date" content="2003-11-24" />
<meta name="date" content="2004-01-11" />
<meta name="copyright" content="Copyright David Abrahams, Jeremy Siek, and Thomas Witt 2003. All rights reserved" />
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<div class="document" id="iterator-facade">
@ -218,7 +27,7 @@ ul.auto-toc {
Lab</a>, University of Hanover <a class="last reference" href="http://www.ive.uni-hannover.de">Institute for Transport
Railway Operation and Construction</a></td></tr>
<tr><th class="docinfo-name">Date:</th>
<td>2003-11-24</td></tr>
<td>2004-01-11</td></tr>
<tr><th class="docinfo-name">Copyright:</th>
<td>Copyright David Abrahams, Jeremy Siek, and Thomas Witt 2003. All rights reserved</td></tr>
</tbody>
@ -244,12 +53,16 @@ and associated types, to be supplied by a derived iterator class.</td>
<li><a class="reference" href="#id2" id="id12" name="id12"><tt class="literal"><span class="pre">operator-&gt;</span></tt></a></li>
</ul>
</li>
<li><a class="reference" href="#tutorial-example" id="id13" name="id13">Tutorial Example</a></li>
<li><a class="reference" href="#reference" id="id14" name="id14">Reference</a><ul>
<li><a class="reference" href="#ref" id="id15" name="id15">Ref</a><ul>
<li><a class="reference" href="#iterator-facade-usage" id="id16" name="id16"><tt class="literal"><span class="pre">iterator_facade</span></tt> usage</a></li>
<li><a class="reference" href="#iterator-facade-iterator-category" id="id17" name="id17"><tt class="literal"><span class="pre">iterator_facade</span></tt> iterator category</a></li>
<li><a class="reference" href="#iterator-facade-operations" id="id18" name="id18"><tt class="literal"><span class="pre">iterator_facade</span></tt> operations</a></li>
<li><a class="reference" href="#tutorial-example" id="id13" name="id13">Tutorial Example</a><ul>
<li><a class="reference" href="#introduction" id="id14" name="id14">Introduction</a></li>
<li><a class="reference" href="#the-problem" id="id15" name="id15">The Problem</a></li>
</ul>
</li>
<li><a class="reference" href="#reference" id="id16" name="id16">Reference</a><ul>
<li><a class="reference" href="#ref" id="id17" name="id17">Ref</a><ul>
<li><a class="reference" href="#iterator-facade-usage" id="id18" name="id18"><tt class="literal"><span class="pre">iterator_facade</span></tt> usage</a></li>
<li><a class="reference" href="#iterator-facade-iterator-category" id="id19" name="id19"><tt class="literal"><span class="pre">iterator_facade</span></tt> iterator category</a></li>
<li><a class="reference" href="#iterator-facade-operations" id="id20" name="id20"><tt class="literal"><span class="pre">iterator_facade</span></tt> operations</a></li>
</ul>
</li>
</ul>
@ -412,14 +225,16 @@ into the temporary iterator <tt class="literal"><span class="pre">p+n</span></tt
<tt class="literal"><span class="pre">operator[]</span></tt> returns.</p>
<p>Writable iterators built with <tt class="literal"><span class="pre">iterator_facade</span></tt> implement the
semantics required by the preferred resolution to <a class="reference" href="http://anubis.dkuug.dk/jtc1/sc22/wg21/docs/lwg-active.html#299">issue 299</a> and
adopted by proposal <a class="reference" href="http://anubis.dkuug.dk/JTC1/SC22/WG21/docs/papers/2003/n1550.html">n1550</a>: the result of <tt class="literal"><span class="pre">p[n]</span></tt> is a proxy object
containing a copy of <tt class="literal"><span class="pre">p+n</span></tt>, and <tt class="literal"><span class="pre">p[n]</span> <span class="pre">=</span> <span class="pre">x</span></tt> is equivalent to <tt class="literal"><span class="pre">*(p</span>
<span class="pre">+</span> <span class="pre">n)</span> <span class="pre">=</span> <span class="pre">x</span></tt>. This approach will work properly for any random-access
iterator regardless of the other details of its implementation. A
user who knows more about the implementation of her iterator is free
to implement an <tt class="literal"><span class="pre">operator[]</span></tt> which returns an lvalue in the derived
iterator class; it will hide the one supplied by <tt class="literal"><span class="pre">iterator_facade</span></tt>
from clients of her iterator.</p>
adopted by proposal <a class="reference" href="http://anubis.dkuug.dk/JTC1/SC22/WG21/docs/papers/2003/n1550.html">n1550</a>: the result of <tt class="literal"><span class="pre">p[n]</span></tt> is an object
convertible to the iterator's <tt class="literal"><span class="pre">value_type</span></tt>, and <tt class="literal"><span class="pre">p[n]</span> <span class="pre">=</span> <span class="pre">x</span></tt> is
equivalent to <tt class="literal"><span class="pre">*(p</span> <span class="pre">+</span> <span class="pre">n)</span> <span class="pre">=</span> <span class="pre">x</span></tt> (Note: This result object may be
implemented as a proxy containing a copy of <tt class="literal"><span class="pre">p+n</span></tt>). This approach
will work properly for any random-access iterator regardless of the
other details of its implementation. A user who knows more about
the implementation of her iterator is free to implement an
<tt class="literal"><span class="pre">operator[]</span></tt> that returns an lvalue in the derived iterator
class; it will hide the one supplied by <tt class="literal"><span class="pre">iterator_facade</span></tt> from
clients of her iterator.</p>
<a class="target" id="operator-arrow" name="operator-arrow"></a></div>
<div class="section" id="id2">
<h2><a class="toc-backref" href="#id12" name="id2"><tt class="literal"><span class="pre">operator-&gt;</span></tt></a></h2>
@ -445,12 +260,82 @@ Patterns, C++ Report, February 1995, pp. 24-27.</td></tr>
</div>
<div class="section" id="tutorial-example">
<h1><a class="toc-backref" href="#id13" name="tutorial-example">Tutorial Example</a></h1>
<p>I'm working on a Tutorial example to go here.</p>
<!-- 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) -->
<div class="section" id="introduction">
<h2><a class="toc-backref" href="#id14" name="introduction">Introduction</a></h2>
<p>In this section we'll walk through the implementation of a few
iterators using <tt class="literal"><span class="pre">iterator_facade</span></tt>, based around the simple
example of a linked list of polymorphic objects.</p>
</div>
<div class="section" id="the-problem">
<h2><a class="toc-backref" href="#id15" name="the-problem">The Problem</a></h2>
<p>Say we've written a polymorphic linked list node as follows:</p>
<pre class="literal-block">
# include &lt;iostream&gt;
struct node_base
{
node_base() : m_next(0) {}
virtual ~node_base() { delete m_next; }
node_base* next() const { return m_next; }
// print to the stream
virtual void print(std::ostream&amp; s) const = 0;
// double the value
virtual void twice() = 0;
void append(node_base* p)
{
if (m_next)
m_next-&gt;append(p);
else
m_next = p;
}
private:
node_base* m_next;
};
</pre>
<p>Lists can hold objects of different types by linking together
specializations of the following template:</p>
<pre class="literal-block">
template &lt;class T&gt;
struct node : node_base
{
node(T x)
: m_value(x)
{}
void print(std::ostream&amp; s) const { s &lt;&lt; this-&gt;m_value; }
void twice() { m_value += m_value; }
private:
T m_value;
};
</pre>
<p>And we can print any node using the following streaming operator:</p>
<pre class="literal-block">
inline std::ostream&amp; operator&lt;&lt;(std::ostream&amp; s, node_base const&amp; n)
{
n.print(s);
return s;
}
</pre>
<div class="sidebar">
<p class="sidebar-title">Note</p>
<p>This is in progress; check the ../example directory for code.</p>
</div>
</div>
</div>
<div class="section" id="reference">
<h1><a class="toc-backref" href="#id14" name="reference">Reference</a></h1>
<h1><a class="toc-backref" href="#id16" name="reference">Reference</a></h1>
<div class="section" id="ref">
<h2><a class="toc-backref" href="#id15" name="ref">Ref</a></h2>
<h2><a class="toc-backref" href="#id17" name="ref">Ref</a></h2>
<p>We need to resolve the title levels here.</p>
<!-- Version 1.3 of this ReStructuredText document corresponds to
n1530_, the paper accepted by the LWG for TR1. -->
@ -563,7 +448,7 @@ struct enable_if_interoperable
{};
</pre>
<div class="section" id="iterator-facade-usage">
<h3><a class="toc-backref" href="#id16" name="iterator-facade-usage"><tt class="literal"><span class="pre">iterator_facade</span></tt> usage</a></h3>
<h3><a class="toc-backref" href="#id18" name="iterator-facade-usage"><tt class="literal"><span class="pre">iterator_facade</span></tt> usage</a></h3>
<p>The following table describes the typical valid expressions on
<tt class="literal"><span class="pre">iterator_facade</span></tt>'s <tt class="literal"><span class="pre">Derived</span></tt> parameter, depending on the
iterator concept(s) it will model. The operations in the first
@ -647,7 +532,7 @@ Iterator</td>
</table>
<a class="target" id="facade-iterator-category" name="facade-iterator-category"></a></div>
<div class="section" id="iterator-facade-iterator-category">
<h3><a class="toc-backref" href="#id17" name="iterator-facade-iterator-category"><tt class="literal"><span class="pre">iterator_facade</span></tt> iterator category</a></h3>
<h3><a class="toc-backref" href="#id19" name="iterator-facade-iterator-category"><tt class="literal"><span class="pre">iterator_facade</span></tt> iterator category</a></h3>
<p>The <tt class="literal"><span class="pre">iterator_category</span></tt> member of <tt class="literal"><span class="pre">iterator_facade&lt;X,V,R,C,D&gt;</span></tt>
is a type which satisfies the following conditions:</p>
<blockquote>
@ -700,7 +585,7 @@ convertible, and not to any more-derived traversal tag type.</p>
</blockquote>
</div>
<div class="section" id="iterator-facade-operations">
<h3><a class="toc-backref" href="#id18" name="iterator-facade-operations"><tt class="literal"><span class="pre">iterator_facade</span></tt> operations</a></h3>
<h3><a class="toc-backref" href="#id20" name="iterator-facade-operations"><tt class="literal"><span class="pre">iterator_facade</span></tt> operations</a></h3>
<p>The operations in this section are described in terms of operations on
the core interface of <tt class="literal"><span class="pre">Derived</span></tt> which may be inaccessible
(i.e. private). The implementation should access these operations
@ -736,10 +621,13 @@ of type <tt class="literal"><span class="pre">pointer</span></tt> equal to:</p>
<col class="field-name" />
<col class="field-body" />
<tbody valign="top">
<tr class="field"><th class="field-name">Returns:</th><td class="field-body">an object convertible to <tt class="literal"><span class="pre">reference</span></tt> and holding a copy
<em>p</em> of <tt class="literal"><span class="pre">*static_cast&lt;Derived</span> <span class="pre">const*&gt;(this)</span> <span class="pre">+</span> <span class="pre">n</span></tt> such that, for a constant object <tt class="literal"><span class="pre">v</span></tt> of type
<tt class="literal"><span class="pre">value_type</span></tt>, <tt class="literal"><span class="pre">(*static_cast&lt;Derived</span> <span class="pre">const*&gt;(this))[n]</span> <span class="pre">=</span> <span class="pre">v</span></tt> is equivalent
to <tt class="literal"><span class="pre">p</span> <span class="pre">=</span> <span class="pre">v</span></tt>.</td>
<tr class="field"><th class="field-name">Returns:</th><td class="field-body">an object convertible to <tt class="literal"><span class="pre">value_type</span></tt>. For constant
objects <tt class="literal"><span class="pre">v</span></tt> of type <tt class="literal"><span class="pre">value_type</span></tt>, and <tt class="literal"><span class="pre">n</span></tt> of type
<tt class="literal"><span class="pre">difference_type</span></tt>, and reference <tt class="literal"><span class="pre">p</span></tt> equal to
<tt class="literal"><span class="pre">*static_cast&lt;Derived</span> <span class="pre">const*&gt;(this)</span></tt>, <tt class="literal"><span class="pre">(*this)[n]</span> <span class="pre">=</span> <span class="pre">v</span></tt> is
equivalent to <tt class="literal"><span class="pre">*(p+</span> <span class="pre">n)</span> <span class="pre">=</span> <span class="pre">v</span></tt>, and <tt class="literal"><span class="pre">static_cast&lt;value_type</span>
<span class="pre">const&amp;&gt;((*this)[n])</span></tt> is equivalent to
<tt class="literal"><span class="pre">static_cast&lt;value_type</span> <span class="pre">const&amp;&gt;(*(p+n))</span></tt></td>
</tr>
</tbody>
</table>
@ -840,11 +728,5 @@ return tmp -= n;
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