1<HTML> 2<!-- 3 Copyright (c) Jeremy Siek 2000 4 5 Distributed under the Boost Software License, Version 1.0. 6 (See accompanying file LICENSE_1_0.txt or copy at 7 http://www.boost.org/LICENSE_1_0.txt) 8 --> 9<Head> 10<Title>LvaluePropertyMap</Title> 11<BODY BGCOLOR="#ffffff" LINK="#0000ee" TEXT="#000000" VLINK="#551a8b" 12 ALINK="#ff0000"> 13<IMG SRC="../../../boost.png" 14 ALT="C++ Boost" width="277" height="86"> 15 16<BR Clear> 17 18<H2><A NAME="concept:LvaluePropertyMap"></A> 19LvaluePropertyMap 20</H2> 21 22The LvaluePropertyMap provides <code>operator[]</code> and function <code>get()</code> for accessing a 23reference to a value object. The return type refines that of function <code>get()</code>in <a 24href="./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). 25 26<H3>Refinement of</H3> 27 28<a href="./ReadablePropertyMap.html">ReadablePropertyMap</a> 29for non-mutable or <a href="./ReadWritePropertyMap.html">ReadWritePropertyMap</a> for mutable property map. 30 31<h3>Notation</h3> 32 33<Table> 34<TR> 35<TD><tt>PMap</tt></TD> 36<TD>A type that is a model of LvaluePropertyMap.</TD> 37</TR> 38<TR> 39<TD><tt>pmap</tt></TD> 40<TD>An object of type <tt>PMap</tt>.</td> 41</TR> 42<TR> 43<TD><tt>key</tt></TD> 44<TD>An object of type <tt>boost::property_traits<PMap>::key_type</tt>.</td> 45</TR> 46 47</table> 48 49 50<h3>Associated Types</h3> 51 52<table border> 53 54<tr> 55<td>Reference Type</td> 56<td><TT>boost::property_traits<PMap>::reference</TT></td> 57<td> 58The reference type, which must be a reference or const reference to 59the value type of the property map. 60</td> 61</tr> 62 63<tr> 64<td>Property Map Category 65<td><TT>boost::property_traits<PMap>::category</TT></td> 66<td> 67The category of the property: a type convertible to 68<TT>boost::lvalue_property_map_tag</TT>. 69</td> 70</tr> 71 72</table> 73 74<h3>Valid Expressions</h3> 75 76<table border> 77<tr> 78<th>Name</th><th>Expression</th><th>Return Type</th><th>Description</th> 79</tr> 80 81 82<tr> 83<td>Access Property Value </td> 84<TD><TT>pmap[key]</TT></TD> 85<TD> 86<TT>value_type&</TT> for mutable, <TT>const value_type&</TT> 87otherwise. 88</TD> 89<TD>Obtain a reference to the value associated with <TT>key</TT>.</TD> 90</TR> 91</TABLE> 92 93<h3>Concept Checking Class</h3> 94 95<pre> template <class PMap, class Key> 96 struct LvaluePropertyMapConcept 97 { 98 typedef typename property_traits<PMap>::category Category; 99 typedef boost::lvalue_property_map_tag LvalueTag; 100 typedef const typename property_traits<PMap>::value_type& const_reference; 101 void constraints() { 102 function_requires< ReadWritePropertyMapConcept<PMap, Key> >(); 103 function_requires< ConvertibleConcept<Category, LvalueTag> >(); 104 105 const_reference ref = pmap[k]; 106 } 107 PMap pmap; 108 Key k; 109 }; 110 111 template <class PMap, class Key> 112 struct Mutable_LvaluePropertyMapConcept 113 { 114 typedef typename property_traits<PMap>::category Category; 115 typedef boost::lvalue_property_map_tag LvalueTag; 116 typedef typename property_traits<PMap>::value_type& reference; 117 void constraints() { 118 function_requires< ReadWritePropertyMapConcept<PMap, Key> >(); 119 function_requires<ConvertibleConcept<Category, LvalueTag> >(); 120 121 reference ref = pmap[k]; 122 } 123 PMap pmap; 124 Key k; 125 };</pre> 126 127<h3>See Also</h3> 128 129<a href="./property_map.html">Property map concepts</a> 130 131 132<br> 133<HR> 134<TABLE> 135<TR valign=top> 136<TD nowrap>Copyright © 2000</TD><TD> 137<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>) 138</TD></TR></TABLE> 139 140</BODY> 141</HTML> 142
