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updated boost from 1_33_1 to 1_34_1
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13<Head>
14<Title>LvaluePropertyMap</Title>
15<BODY BGCOLOR="#ffffff" LINK="#0000ee" TEXT="#000000" VLINK="#551a8b" 
16        ALINK="#ff0000"> 
17<IMG SRC="../../boost.png" 
18     ALT="C++ Boost" width="277" height="86"> 
19
20<BR Clear>
21
22<H2><A NAME="concept:LvaluePropertyMap"></A>
23LvaluePropertyMap
24</H2>
25
26The LvaluePropertyMap provides an interface for accessing a
27reference to a property object (instead of a copy of the object as in
28the <TT>get()</TT> function required by <a
29href="./ReadablePropertyMap.html">ReadablePropertyMap</a>). An
30LvaluePropertyMap can be <I>mutable</I> or
31<I>non-mutable</I>. The mutable LvaluePropertyMap returns a
32reference whereas the non-mutable returns a const reference.
33
34<H3>Refinement of</H3>
35
36<a href="./ReadablePropertyMap.html">ReadablePropertyMap</a>
37for non-mutable or <a href="./ReadWritePropertyMap.html">ReadWritePropertyMap</a> for mutable property map.
38
39<h3>Notation</h3>
40
41<Table>
42<TR>
43<TD><tt>PMap</tt></TD>
44<TD>A type that is a model of LvaluePropertyMap.</TD>
45</TR>
46<TR>
47<TD><tt>pmap</tt></TD>
48<TD>An object of type <tt>PMap</tt>.</td>
49</TR>
50<TR>
51<TD><tt>key</tt></TD>
52<TD>An object of type <tt>boost::property_traits&lt;PMap&gt;::key_type</tt>.</td>
53</TR>
54
55</table>
56
57
58<h3>Associated Types</h3>
59
60<table border>
61
62<tr>
63<td>Reference Type</td>
64<td><TT>boost::property_traits&lt;PMap&gt;::reference</TT></td> 
65<td>
66The reference type, which must be a reference or const reference to
67the value typeof the property map.
68</td>
69</tr>
70
71<tr>
72<td>Property Map Category
73<td><TT>boost::property_traits&lt;PMap&gt;::category</TT></td> 
74<td>
75The category of the property: a type convertible to
76<TT>boost::lvalue_property_map_tag</TT>.
77</td>
78</tr>
79
80</table>
81
82<h3>Valid Expressions</h3>
83
84<table border>
85<tr>
86<th>Name</th><th>Expression</th><th>Return Type</th><th>Description</th>
87</tr>
88
89
90<tr>
91<td>Access Property Value </td>
92<TD><TT>pmap[key]</TT></TD>
93<TD>
94<TT>value_type&amp;</TT> for mutable, <TT>const value_type&amp;</TT>
95otherwise.
96</TD>
97<TD>Obtain a reference to the property identified by <TT>key</TT>.</TD>
98</TR>
99</TABLE>
100
101<h3>Concept Checking Class</h3>
102
103<pre>  template &lt;class PMap, class Key&gt;
104  struct LvaluePropertyMapConcept
105  {
106    typedef typename property_traits&lt;PMap&gt;::category Category;
107    typedef boost::lvalue_property_map_tag LvalueTag;
108    typedef const typename property_traits&lt;PMap&gt;::value_type&amp; const_reference;
109    void constraints() {
110      function_requires&lt; ReadWritePropertyMapConcept&lt;PMap, Key&gt; &gt;();
111      function_requires&lt; ConvertibleConcept&lt;Category, LvalueTag&gt; &gt;();
112
113      const_reference ref = pmap[k];
114    }
115    PMap pmap;
116    Key k;
117  };
118
119  template &lt;class PMap, class Key&gt;
120  struct Mutable_LvaluePropertyMapConcept
121  {
122    typedef typename property_traits&lt;PMap&gt;::category Category;
123    typedef boost::lvalue_property_map_tag LvalueTag;
124    typedef typename property_traits&lt;PMap&gt;::value_type&amp; reference;
125    void constraints() {
126      function_requires&lt; ReadWritePropertyMapConcept&lt;PMap, Key&gt; &gt;();
127      function_requires&lt;ConvertibleConcept&lt;Category, LvalueTag&gt; &gt;();
128
129      reference ref = pmap[k];
130    }
131    PMap pmap;
132    Key k;
133  };</pre>
134
135<h3>See Also</h3>
136
137<a href="./property_map.html">Property map concepts</a>
138
139
140<br>
141<HR>
142<TABLE>
143<TR valign=top>
144<TD nowrap>Copyright &copy 2000</TD><TD>
145<a HREF="../../people/jeremy_siek.htm">Jeremy Siek</a>, Univ.of Notre Dame (<A HREF="mailto:jsiek@lsc.nd.edu">jsiek@lsc.nd.edu</A>)
146</TD></TR></TABLE>
147
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