2004-01-13 23:03:18 +00:00
<?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" / >
2006-09-11 22:27:29 +00:00
< meta name = "generator" content = "Docutils 0.4: http://docutils.sourceforge.net/" / >
2004-01-13 23:03:18 +00:00
< title > pointee and indirect_reference< / title >
< meta name = "author" content = "David Abrahams" / >
< meta name = "organization" content = "Boost Consulting" / >
2005-05-20 15:32:55 +00:00
< meta name = "date" content = "2005-02-27" / >
2004-11-02 14:31:27 +00:00
< meta name = "copyright" content = "Copyright David Abrahams 2004." / >
2006-09-11 22:27:29 +00:00
< 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 >
2004-01-13 23:03:18 +00:00
< / head >
< body >
2005-05-20 15:32:55 +00:00
< 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 >
2004-01-13 23:03:18 +00:00
< 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 >
2004-01-29 05:55:26 +00:00
< td > < a class = "first last reference" href = "mailto:dave@boost-consulting.com" > dave@ boost-consulting.com< / a > < / td > < / tr >
2004-01-13 23:03:18 +00:00
< 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 >
2005-05-20 15:32:55 +00:00
< td > 2005-02-27< / td > < / tr >
2004-01-13 23:03:18 +00:00
< tr > < th class = "docinfo-name" > Copyright:< / th >
2004-11-02 14:31:27 +00:00
< td > Copyright David Abrahams 2004.< / td > < / tr >
2004-01-13 23:03:18 +00:00
< / tbody >
< / table >
2006-09-11 22:27:29 +00:00
<!-- 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) -->
2005-05-20 15:32:55 +00:00
< table class = "docutils field-list" frame = "void" rules = "none" >
2004-01-13 23:03:18 +00:00
< 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 >
2006-09-11 22:27:29 +00:00
< div class = "section" >
< h1 > < a id = "overview" name = "overview" > Overview< / a > < / h1 >
2004-01-13 23:03:18 +00:00
< 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 >
2006-09-11 22:27:29 +00:00
< div class = "section" >
< h2 > < a id = "pointee" name = "pointee" > < tt class = "docutils literal" > < span class = "pre" > pointee< / span > < / tt > < / a > < / h2 >
2004-01-13 23:03:18 +00:00
< 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
2005-05-20 15:32:55 +00:00
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
2004-01-13 23:03:18 +00:00
for all pointers, standard and boost smart pointers, and
iterators), and when it guesses wrongly, it can be specialized as
2005-02-27 17:28:24 +00:00
necessary:< / p >
2004-01-13 23:03:18 +00:00
< pre class = "literal-block" >
namespace boost
{
template < class T>
struct pointee< third_party_lib::smart_pointer< T> >
{
typedef T type;
};
}
< / pre >
< / div >
2006-09-11 22:27:29 +00:00
< div class = "section" >
< h2 > < a id = "indirect-reference" name = "indirect-reference" > < tt class = "docutils literal" > < span class = "pre" > indirect_reference< / span > < / tt > < / a > < / h2 >
2005-05-20 15:32:55 +00:00
< 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
2004-01-13 23:03:18 +00:00
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
2005-05-20 15:32:55 +00:00
information is needed, call on < tt class = "docutils literal" > < span class = "pre" > indirect_reference< / span > < / tt > .< / p >
2004-01-13 23:03:18 +00:00
< p > Both of these templates are essential to the correct functioning of
2005-05-20 15:32:55 +00:00
< a class = "reference" href = "indirect_iterator.html" > < tt class = "docutils literal" > < span class = "pre" > indirect_iterator< / span > < / tt > < / a > .< / p >
2004-01-13 23:03:18 +00:00
< / div >
< / div >
2006-09-11 22:27:29 +00:00
< 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 >
2004-01-13 23:03:18 +00:00
<!-- 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 >
2005-05-20 15:32:55 +00:00
< table class = "docutils field-list" frame = "void" rules = "none" >
2004-01-13 23:03:18 +00:00
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
2005-05-20 15:32:55 +00:00
< 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
2004-01-13 23:03:18 +00:00
ambiguous nor shall it violate access control, and
2005-05-20 15:32:55 +00:00
< 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
2004-01-13 23:03:18 +00:00
be well formed. [Note: These requirements need not apply to
2005-05-20 15:32:55 +00:00
explicit or partial specializations of < tt class = "docutils literal" > < span class = "pre" > pointee< / span > < / tt > ]< / td >
2004-01-13 23:03:18 +00:00
< / tr >
< / tbody >
< / table >
2005-05-20 15:32:55 +00:00
< 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 >
2004-01-13 23:03:18 +00:00
< 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 >
2006-09-11 22:27:29 +00:00
< div class = "section" >
< h2 > < a id = "id2" name = "id2" > < tt class = "docutils literal" > < span class = "pre" > indirect_reference< / span > < / tt > < / a > < / h2 >
2004-01-13 23:03:18 +00:00
<!-- 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 >
2005-05-20 15:32:55 +00:00
< table class = "docutils field-list" frame = "void" rules = "none" >
2004-01-13 23:03:18 +00:00
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
2005-05-20 15:32:55 +00:00
< 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
2004-01-13 23:03:18 +00:00
ambiguous nor shall it violate access control, and
2005-05-20 15:32:55 +00:00
< 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
2004-01-13 23:03:18 +00:00
be well formed. [Note: These requirements need not apply to
2005-05-20 15:32:55 +00:00
explicit or partial specializations of < tt class = "docutils literal" > < span class = "pre" > indirect_reference< / span > < / tt > ]< / td >
2004-01-13 23:03:18 +00:00
< / tr >
< / tbody >
< / table >
2005-05-20 15:32:55 +00:00
< 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 >
2004-01-13 23:03:18 +00:00
< pre class = "literal-block" >
if ( ++x is ill-formed )
return ``pointee< Dereferenceable> ::type& ``
else
2004-01-14 04:48:53 +00:00
std::iterator_traits< Dereferenceable> ::reference
2004-01-13 23:03:18 +00:00
< / pre >
< / div >
< / div >
< / div >
< / body >
< / html >
