142 lines
3.7 KiB
HTML
142 lines
3.7 KiB
HTML
<HTML>
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<!--
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Copyright (c) Jeremy Siek 2000
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Distributed under the Boost Software License, Version 1.0.
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(See accompanying file LICENSE_1_0.txt or copy at
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http://www.boost.org/LICENSE_1_0.txt)
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-->
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<Head>
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<Title>LvaluePropertyMap</Title>
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<BODY BGCOLOR="#ffffff" LINK="#0000ee" TEXT="#000000" VLINK="#551a8b"
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ALINK="#ff0000">
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<IMG SRC="../../../boost.png"
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ALT="C++ Boost" width="277" height="86">
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<BR Clear>
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<H2><A NAME="concept:LvaluePropertyMap"></A>
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LvaluePropertyMap
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</H2>
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The LvaluePropertyMap provides <code>operator[]</code> and function <code>get()</code> for accessing a
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reference to a value object. The return type refines that of function <code>get()</code>in <a
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href="./ReadablePropertyMap.html">ReadablePropertyMap</a>; it can only be a reference (for a <I>mutable</I> LvaluePropertyMap) or a const reference (for a <I>non-mutable</I> LvaluePropertyMap).
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<H3>Refinement of</H3>
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<a href="./ReadablePropertyMap.html">ReadablePropertyMap</a>
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for non-mutable or <a href="./ReadWritePropertyMap.html">ReadWritePropertyMap</a> for mutable property map.
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<h3>Notation</h3>
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<Table>
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<TR>
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<TD><tt>PMap</tt></TD>
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<TD>A type that is a model of LvaluePropertyMap.</TD>
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</TR>
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<TR>
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<TD><tt>pmap</tt></TD>
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<TD>An object of type <tt>PMap</tt>.</td>
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</TR>
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<TR>
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<TD><tt>key</tt></TD>
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<TD>An object of type <tt>boost::property_traits<PMap>::key_type</tt>.</td>
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</TR>
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</table>
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<h3>Associated Types</h3>
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<table border>
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<tr>
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<td>Reference Type</td>
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<td><TT>boost::property_traits<PMap>::reference</TT></td>
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<td>
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The reference type, which must be a reference or const reference to
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the value type of the property map.
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</td>
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</tr>
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<tr>
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<td>Property Map Category
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<td><TT>boost::property_traits<PMap>::category</TT></td>
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<td>
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The category of the property: a type convertible to
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<TT>boost::lvalue_property_map_tag</TT>.
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</td>
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</tr>
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</table>
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<h3>Valid Expressions</h3>
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<table border>
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<tr>
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<th>Name</th><th>Expression</th><th>Return Type</th><th>Description</th>
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</tr>
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<tr>
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<td>Access Property Value </td>
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<TD><TT>pmap[key]</TT></TD>
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<TD>
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<TT>value_type&</TT> for mutable, <TT>const value_type&</TT>
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otherwise.
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</TD>
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<TD>Obtain a reference to the value associated with <TT>key</TT>.</TD>
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</TR>
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</TABLE>
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<h3>Concept Checking Class</h3>
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<pre> template <class PMap, class Key>
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struct LvaluePropertyMapConcept
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{
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typedef typename property_traits<PMap>::category Category;
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typedef boost::lvalue_property_map_tag LvalueTag;
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typedef const typename property_traits<PMap>::value_type& const_reference;
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void constraints() {
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function_requires< ReadWritePropertyMapConcept<PMap, Key> >();
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function_requires< ConvertibleConcept<Category, LvalueTag> >();
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const_reference ref = pmap[k];
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}
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PMap pmap;
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Key k;
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};
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template <class PMap, class Key>
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struct Mutable_LvaluePropertyMapConcept
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{
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typedef typename property_traits<PMap>::category Category;
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typedef boost::lvalue_property_map_tag LvalueTag;
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typedef typename property_traits<PMap>::value_type& reference;
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void constraints() {
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function_requires< ReadWritePropertyMapConcept<PMap, Key> >();
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function_requires<ConvertibleConcept<Category, LvalueTag> >();
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reference ref = pmap[k];
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}
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PMap pmap;
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Key k;
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};</pre>
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<h3>See Also</h3>
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<a href="./property_map.html">Property map concepts</a>
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<br>
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<HR>
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<TABLE>
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<TR valign=top>
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<TD nowrap>Copyright © 2000</TD><TD>
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<a HREF="http://www.boost.org/people/jeremy_siek.htm">Jeremy Siek</a>, Univ.of Notre Dame (<A HREF="mailto:jsiek@lsc.nd.edu">jsiek@lsc.nd.edu</A>)
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</TD></TR></TABLE>
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</BODY>
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</HTML>
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