feedc0de/boost_iterator
1
0
Fork 0
forked from boostorg/iterator
Code Pull Requests Activity
Files
aa483f4961157f5ab8cb1594dbd8f854544ce668
boost_iterator/doc/pointee.html
Dave Abrahams 5184d64b80 Add missing license/copyright 
[SVN r35070]
2006-09-11 22:27:29 +00:00

460 lines
14 KiB
HTML
Executable File
Raw Blame History

<?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 0.4: 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="2005-02-27" />
<meta name="copyright" content="Copyright David Abrahams 2004." />
<style type="text/css">
/*
:Author: David Goodger
:Contact: goodger@users.sourceforge.net
:Date: $Date$
:Revision: $Revision$
:Copyright: This stylesheet has been placed in the public domain.
Default cascading style sheet for the HTML output of Docutils.
See http://docutils.sf.net/docs/howto/html-stylesheets.html for how to
customize this style sheet.
*/
/* used to remove borders from tables and images */
.borderless, table.borderless td, table.borderless th {
border: 0 }
table.borderless td, table.borderless th {
/* Override padding for "table.docutils td" with "! important".
The right padding separates the table cells. */
padding: 0 0.5em 0 0 ! important }
.first {
/* Override more specific margin styles with "! important". */
margin-top: 0 ! important }
.last, .with-subtitle {
margin-bottom: 0 ! important }
.hidden {
display: none }
a.toc-backref {
text-decoration: none ;
color: black }
blockquote.epigraph {
margin: 2em 5em ; }
dl.docutils dd {
margin-bottom: 0.5em }
/* Uncomment (and remove this text!) to get bold-faced definition list terms
dl.docutils dt {
font-weight: bold }
*/
div.abstract {
margin: 2em 5em }
div.abstract p.topic-title {
font-weight: bold ;
text-align: center }
div.admonition, div.attention, div.caution, div.danger, div.error,
div.hint, div.important, div.note, div.tip, div.warning {
margin: 2em ;
border: medium outset ;
padding: 1em }
div.admonition p.admonition-title, div.hint p.admonition-title,
div.important p.admonition-title, div.note p.admonition-title,
div.tip p.admonition-title {
font-weight: bold ;
font-family: sans-serif }
div.attention p.admonition-title, div.caution p.admonition-title,
div.danger p.admonition-title, div.error p.admonition-title,
div.warning p.admonition-title {
color: red ;
font-weight: bold ;
font-family: sans-serif }
/* Uncomment (and remove this text!) to get reduced vertical space in
compound paragraphs.
div.compound .compound-first, div.compound .compound-middle {
margin-bottom: 0.5em }
div.compound .compound-last, div.compound .compound-middle {
margin-top: 0.5em }
*/
div.dedication {
margin: 2em 5em ;
text-align: center ;
font-style: italic }
div.dedication p.topic-title {
font-weight: bold ;
font-style: normal }
div.figure {
margin-left: 2em ;
margin-right: 2em }
div.footer, div.header {
clear: both;
font-size: smaller }
div.line-block {
display: block ;
margin-top: 1em ;
margin-bottom: 1em }
div.line-block div.line-block {
margin-top: 0 ;
margin-bottom: 0 ;
margin-left: 1.5em }
div.sidebar {
margin-left: 1em ;
border: medium outset ;
padding: 1em ;
background-color: #ffffee ;
width: 40% ;
float: right ;
clear: right }
div.sidebar p.rubric {
font-family: sans-serif ;
font-size: medium }
div.system-messages {
margin: 5em }
div.system-messages h1 {
color: red }
div.system-message {
border: medium outset ;
padding: 1em }
div.system-message p.system-message-title {
color: red ;
font-weight: bold }
div.topic {
margin: 2em }
h1.section-subtitle, h2.section-subtitle, h3.section-subtitle,
h4.section-subtitle, h5.section-subtitle, h6.section-subtitle {
margin-top: 0.4em }
h1.title {
text-align: center }
h2.subtitle {
text-align: center }
hr.docutils {
width: 75% }
img.align-left {
clear: left }
img.align-right {
clear: right }
ol.simple, ul.simple {
margin-bottom: 1em }
ol.arabic {
list-style: decimal }
ol.loweralpha {
list-style: lower-alpha }
ol.upperalpha {
list-style: upper-alpha }
ol.lowerroman {
list-style: lower-roman }
ol.upperroman {
list-style: upper-roman }
p.attribution {
text-align: right ;
margin-left: 50% }
p.caption {
font-style: italic }
p.credits {
font-style: italic ;
font-size: smaller }
p.label {
white-space: nowrap }
p.rubric {
font-weight: bold ;
font-size: larger ;
color: maroon ;
text-align: center }
p.sidebar-title {
font-family: sans-serif ;
font-weight: bold ;
font-size: larger }
p.sidebar-subtitle {
font-family: sans-serif ;
font-weight: bold }
p.topic-title {
font-weight: bold }
pre.address {
margin-bottom: 0 ;
margin-top: 0 ;
font-family: serif ;
font-size: 100% }
pre.literal-block, pre.doctest-block {
margin-left: 2em ;
margin-right: 2em ;
background-color: #eeeeee }
span.classifier {
font-family: sans-serif ;
font-style: oblique }
span.classifier-delimiter {
font-family: sans-serif ;
font-weight: bold }
span.interpreted {
font-family: sans-serif }
span.option {
white-space: nowrap }
span.pre {
white-space: pre }
span.problematic {
color: red }
span.section-subtitle {
/* font-size relative to parent (h1..h6 element) */
font-size: 80% }
table.citation {
border-left: solid 1px gray;
margin-left: 1px }
table.docinfo {
margin: 2em 4em }
table.docutils {
margin-top: 0.5em ;
margin-bottom: 0.5em }
table.footnote {
border-left: solid 1px black;
margin-left: 1px }
table.docutils td, table.docutils th,
table.docinfo td, table.docinfo th {
padding-left: 0.5em ;
padding-right: 0.5em ;
vertical-align: top }
table.docutils th.field-name, table.docinfo th.docinfo-name {
font-weight: bold ;
text-align: left ;
white-space: nowrap ;
padding-left: 0 }
h1 tt.docutils, h2 tt.docutils, h3 tt.docutils,
h4 tt.docutils, h5 tt.docutils, h6 tt.docutils {
font-size: 100% }
tt.docutils {
background-color: #eeeeee }
ul.auto-toc {
list-style-type: none }
</style>
</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" 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" href="http://www.boost-consulting.com">Boost Consulting</a></td></tr>
<tr><th class="docinfo-name">Date:</th>
<td>2005-02-27</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">
<h1><a id="overview" name="overview">Overview</a></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">
<h2><a id="pointee" name="pointee"><tt class="docutils literal"><span class="pre">pointee</span></tt></a></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">
<h2><a id="indirect-reference" name="indirect-reference"><tt class="docutils literal"><span class="pre">indirect_reference</span></tt></a></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" href="indirect_iterator.html"><tt class="docutils literal"><span class="pre">indirect_iterator</span></tt></a>.</p>
</div>
</div>
<div class="section">
<h1><a id="reference" name="reference">Reference</a></h1>
<div class="section">
<h2><a id="id1" name="id1"><tt class="docutils literal"><span class="pre">pointee</span></tt></a></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">
<h2><a id="id2" name="id2"><tt class="docutils literal"><span class="pre">indirect_reference</span></tt></a></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>
</body>
</html>
View Git Blame Copy Permalink