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| 2 | <!-- |
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| 3 | -- Copyright (c) Jeremy Siek 2000 |
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| 5 | -- Permission to use, copy, modify, distribute and sell this software |
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| 6 | -- and its documentation for any purpose is hereby granted without fee, |
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| 9 | -- in supporting documentation. Silicon Graphics makes no |
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| 11 | -- purpose. It is provided "as is" without express or implied warranty. |
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| 12 | --> |
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| 13 | <Head> |
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| 14 | <Title>Readable Property Map</Title> |
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| 15 | <BODY BGCOLOR="#ffffff" LINK="#0000ee" TEXT="#000000" VLINK="#551a8b" |
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| 16 | ALINK="#ff0000"> |
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| 17 | <IMG SRC="../../boost.png" |
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| 18 | ALT="C++ Boost" width="277" height="86"> |
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| 19 | |
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| 20 | <BR Clear> |
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| 21 | |
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| 22 | |
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| 23 | <H2><A NAME="concept:ReadablePropertyMap"></A> |
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| 24 | Readable Property Map |
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| 25 | </H2> |
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| 26 | |
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| 27 | A Readable Property Map provides read-access to the value object associated with a given key via a call to the <tt>get()</tt> function. |
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| 28 | The <tt>get()</tt> function returns a copy of the value object. |
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| 29 | |
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| 30 | <h3>Refinement of</h3> |
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| 31 | |
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| 32 | <a href="../utility/CopyConstructible.html">Copy Constructible</a> |
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| 33 | |
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| 34 | <h3>Notation</h3> |
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| 35 | |
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| 36 | <Table> |
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| 37 | <TR> |
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| 38 | <TD><tt>PMap</tt></TD> |
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| 39 | <TD>A type that is a model of Readable Property Map.</TD> |
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| 40 | </TR> |
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| 41 | <TR> |
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| 42 | <TD><tt>pmap</tt></TD> |
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| 43 | <TD>An object of type <tt>PMap</tt>.</td> |
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| 44 | </TR> |
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| 45 | <TR> |
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| 46 | <TD><tt>key</tt></TD> |
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| 47 | <TD>An object of type <tt>boost::property_traits<PMap>::key_type</tt>.</td> |
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| 48 | </TR> |
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| 49 | |
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| 50 | </table> |
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| 51 | |
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| 52 | <h3>Associated Types</h3> |
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| 53 | |
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| 54 | <table border> |
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| 55 | |
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| 56 | <tr> |
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| 57 | <td>Value Type</td> |
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| 58 | <td><TT>boost::property_traits<PMap>::value_type</TT></td> |
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| 59 | <td>The type of the property.</td> |
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| 60 | </tr> |
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| 61 | |
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| 62 | <tr> |
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| 63 | <td>Reference Type</td> |
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| 64 | <td><TT>boost::property_traits<PMap>::reference</TT></td> |
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| 65 | <td> |
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| 66 | A type that is convertible to the value type. |
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| 67 | </td> |
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| 68 | </tr> |
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| 69 | |
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| 70 | <tr> |
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| 71 | <td>Key Type</td> |
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| 72 | <td><TT>boost::property_traits<PMap>::key_type</TT></td> |
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| 73 | <td> |
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| 74 | The type of the key object used to look up the property. The property |
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| 75 | map may be templated on the key type, in which case this |
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| 76 | typedef can be <TT>void</TT>. |
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| 77 | </td> |
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| 78 | </tr> |
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| 79 | |
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| 80 | <tr> |
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| 81 | <td>Property Map Category</td> |
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| 82 | <td><TT>boost::property_traits<PMap>::category</TT></td> |
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| 83 | <td> |
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| 84 | The category of the property: a type convertible to |
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| 85 | <TT>readable_property_map_tag</TT>. |
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| 86 | </td> |
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| 87 | </tr> |
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| 88 | |
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| 89 | </table> |
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| 90 | |
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| 91 | <h3>Valid Expressions</h3> |
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| 92 | |
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| 93 | <table border> |
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| 94 | <tr> |
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| 95 | <th>Name</th><th>Expression</th><th>Return Type</th><th>Description</th> |
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| 96 | </tr> |
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| 97 | |
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| 98 | <tr> |
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| 99 | <td>Get Property Value </td> |
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| 100 | <TD><TT>get(pmap, key)</TT></TD> |
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| 101 | <TD><TT>reference</TT></TD> |
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| 102 | <TD>Lookup the property of the object identified by <TT>key</TT>.</TD> |
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| 103 | </TR> |
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| 104 | |
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| 105 | </TABLE> |
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| 106 | |
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| 107 | <h3>Concept Checking Class</h3> |
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| 108 | |
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| 109 | <pre> template <class PMap, class Key> |
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| 110 | struct ReadablePropertyMapConcept |
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| 111 | { |
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| 112 | typedef typename property_traits<PMap>::key_type key_type; |
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| 113 | typedef typename property_traits<PMap>::category Category; |
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| 114 | typedef boost::readable_property_map_tag ReadableTag; |
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| 115 | void constraints() { |
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| 116 | function_requires< ConvertibleConcept<Category, ReadableTag> >(); |
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| 117 | |
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| 118 | val = get(pmap, k); |
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| 119 | } |
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| 120 | PMap pmap; |
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| 121 | Key k; |
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| 122 | typename property_traits<PMap>::value_type val; |
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| 123 | };</pre> |
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| 124 | |
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| 125 | <h3>See Also</h3> |
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| 126 | |
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| 127 | <a href="./property_map.html">Property map concepts</a> |
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| 128 | |
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| 129 | <h3>Design Notes</h3> |
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| 130 | |
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| 131 | At various times the name "read-only" was considered for |
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| 132 | this concept. However, that name is inappropriate because concepts are |
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| 133 | inherently positive, not negative. This becomes obvious when we define |
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| 134 | the Read Write Property Map, which refines both the Readable Property |
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| 135 | Map and the Writable Property Map concept. It would not make much |
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| 136 | sense to combine "read-only" and "write-only" |
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| 137 | concepts! |
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| 138 | |
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| 139 | <br> |
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| 140 | <HR> |
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| 141 | <TABLE> |
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| 142 | <TR valign=top> |
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| 143 | <TD nowrap>Copyright © 2000</TD><TD> |
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| 144 | <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>) |
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| 145 | </TD></TR></TABLE> |
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| 146 | |
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| 147 | </BODY> |
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| 148 | </HTML> |
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