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| <Head> |
| <Title>LvaluePropertyMap</Title> |
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| |
| <H2><A NAME="concept:LvaluePropertyMap"></A> |
| LvaluePropertyMap |
| </H2> |
| |
| The LvaluePropertyMap provides an interface for accessing a |
| reference to a property object (instead of a copy of the object as in |
| the <TT>get()</TT> function required by <a |
| href="./ReadablePropertyMap.html">ReadablePropertyMap</a>). An |
| LvaluePropertyMap can be <I>mutable</I> or |
| <I>non-mutable</I>. The mutable LvaluePropertyMap returns a |
| reference whereas the non-mutable returns a const reference. |
| |
| <H3>Refinement of</H3> |
| |
| <a href="./ReadablePropertyMap.html">ReadablePropertyMap</a> |
| for non-mutable or <a href="./ReadWritePropertyMap.html">ReadWritePropertyMap</a> for mutable property map. |
| |
| <h3>Notation</h3> |
| |
| <Table> |
| <TR> |
| <TD><tt>PMap</tt></TD> |
| <TD>A type that is a model of LvaluePropertyMap.</TD> |
| </TR> |
| <TR> |
| <TD><tt>pmap</tt></TD> |
| <TD>An object of type <tt>PMap</tt>.</td> |
| </TR> |
| <TR> |
| <TD><tt>key</tt></TD> |
| <TD>An object of type <tt>boost::property_traits<PMap>::key_type</tt>.</td> |
| </TR> |
| |
| </table> |
| |
| |
| <h3>Associated Types</h3> |
| |
| <table border> |
| |
| <tr> |
| <td>Reference Type</td> |
| <td><TT>boost::property_traits<PMap>::reference</TT></td> |
| <td> |
| The reference type, which must be a reference or const reference to |
| the value typeof the property map. |
| </td> |
| </tr> |
| |
| <tr> |
| <td>Property Map Category |
| <td><TT>boost::property_traits<PMap>::category</TT></td> |
| <td> |
| The category of the property: a type convertible to |
| <TT>boost::lvalue_property_map_tag</TT>. |
| </td> |
| </tr> |
| |
| </table> |
| |
| <h3>Valid Expressions</h3> |
| |
| <table border> |
| <tr> |
| <th>Name</th><th>Expression</th><th>Return Type</th><th>Description</th> |
| </tr> |
| |
| |
| <tr> |
| <td>Access Property Value </td> |
| <TD><TT>pmap[key]</TT></TD> |
| <TD> |
| <TT>value_type&</TT> for mutable, <TT>const value_type&</TT> |
| otherwise. |
| </TD> |
| <TD>Obtain a reference to the property identified by <TT>key</TT>.</TD> |
| </TR> |
| </TABLE> |
| |
| <h3>Concept Checking Class</h3> |
| |
| <pre> template <class PMap, class Key> |
| struct LvaluePropertyMapConcept |
| { |
| typedef typename property_traits<PMap>::category Category; |
| typedef boost::lvalue_property_map_tag LvalueTag; |
| typedef const typename property_traits<PMap>::value_type& const_reference; |
| void constraints() { |
| function_requires< ReadWritePropertyMapConcept<PMap, Key> >(); |
| function_requires< ConvertibleConcept<Category, LvalueTag> >(); |
| |
| const_reference ref = pmap[k]; |
| } |
| PMap pmap; |
| Key k; |
| }; |
| |
| template <class PMap, class Key> |
| struct Mutable_LvaluePropertyMapConcept |
| { |
| typedef typename property_traits<PMap>::category Category; |
| typedef boost::lvalue_property_map_tag LvalueTag; |
| typedef typename property_traits<PMap>::value_type& reference; |
| void constraints() { |
| function_requires< ReadWritePropertyMapConcept<PMap, Key> >(); |
| function_requires<ConvertibleConcept<Category, LvalueTag> >(); |
| |
| reference ref = pmap[k]; |
| } |
| PMap pmap; |
| Key k; |
| };</pre> |
| |
| <h3>See Also</h3> |
| |
| <a href="./property_map.html">Property map concepts</a> |
| |
| |
| <br> |
| <HR> |
| <TABLE> |
| <TR valign=top> |
| <TD nowrap>Copyright © 2000</TD><TD> |
| <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>) |
| </TD></TR></TABLE> |
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