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| 7 | |
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| 8 | <title>Collection</title> |
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| 10 | |
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| 11 | <body bgcolor="#FFFFFF" link="#0000EE" text="#000000" vlink="#551A8B" alink= |
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| 12 | "#FF0000"> |
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| 13 | <h1><img src="../../boost.png" alt="boost logo" width="277" align="middle" |
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| 14 | height="86"><br> |
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| 15 | Collection</h1> |
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| 16 | |
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| 17 | <h3>Description</h3> |
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| 18 | |
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| 19 | <p>A Collection is a <i>concept</i> similar to the STL <a href= |
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| 20 | "http://www.sgi.com/tech/stl/Container.html">Container</a> concept. A |
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| 21 | Collection provides iterators for accessing a range of elements and |
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| 22 | provides information about the number of elements in the Collection. |
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| 23 | However, a Collection has fewer requirements than a Container. The |
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| 24 | motivation for the Collection concept is that there are many useful |
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| 25 | Container-like types that do not meet the full requirements of Container, |
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| 26 | and many algorithms that can be written with this reduced set of |
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| 27 | requirements. To summarize the reduction in requirements:</p> |
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| 28 | |
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| 29 | <ul> |
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| 30 | <li>It is not required to "own" its elements: the lifetime of an element |
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| 31 | in a Collection does not have to match the lifetime of the Collection |
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| 32 | object, though the lifetime of the element should cover the lifetime of |
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| 33 | the Collection object.</li> |
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| 34 | |
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| 35 | <li>The semantics of copying a Collection object is not defined (it could |
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| 36 | be a deep or shallow copy or not even support copying).</li> |
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| 37 | |
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| 38 | <li>The associated reference type of a Collection does not have to be a |
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| 39 | real C++ reference.</li> |
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| 40 | </ul>Because of the reduced requirements, some care must be taken when |
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| 41 | writing code that is meant to be generic for all Collection types. In |
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| 42 | particular, a Collection object should be passed by-reference since |
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| 43 | assumptions can not be made about the behaviour of the copy constructor. |
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| 44 | |
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| 45 | <h3>Associated types</h3> |
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| 46 | |
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| 47 | <table border summary=""> |
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| 48 | <tr> |
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| 49 | <td valign="top">Value type</td> |
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| 50 | |
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| 51 | <td valign="top"><tt>X::value_type</tt></td> |
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| 52 | |
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| 53 | <td valign="top">The type of the object stored in a Collection. If the |
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| 54 | Collection is <i>mutable</i> then the value type must be <a href= |
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| 55 | "http://www.sgi.com/tech/stl/Assignable.html">Assignable</a>. Otherwise |
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| 56 | the value type must be <a href= |
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| 57 | "./CopyConstructible.html">CopyConstructible</a>.</td> |
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| 58 | </tr> |
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| 59 | |
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| 60 | <tr> |
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| 61 | <td valign="top">Iterator type</td> |
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| 62 | |
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| 63 | <td valign="top"><tt>X::iterator</tt></td> |
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| 64 | |
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| 65 | <td valign="top">The type of iterator used to iterate through a |
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| 66 | Collection's elements. The iterator's value type is expected to be the |
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| 67 | Collection's value type. A conversion from the iterator type to the |
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| 68 | const iterator type must exist. The iterator type must be an <a href= |
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| 69 | "http://www.sgi.com/tech/stl/InputIterator.html">InputIterator</a>.</td> |
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| 70 | </tr> |
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| 71 | |
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| 72 | <tr> |
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| 73 | <td valign="top">Const iterator type</td> |
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| 74 | |
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| 75 | <td valign="top"><tt>X::const_iterator</tt></td> |
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| 76 | |
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| 77 | <td valign="top">A type of iterator that may be used to examine, but |
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| 78 | not to modify, a Collection's elements.</td> |
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| 79 | </tr> |
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| 80 | |
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| 81 | <tr> |
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| 82 | <td valign="top">Reference type</td> |
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| 83 | |
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| 84 | <td valign="top"><tt>X::reference</tt></td> |
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| 85 | |
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| 86 | <td valign="top">A type that behaves like a reference to the |
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| 87 | Collection's value type. <a href="#n1">[1]</a></td> |
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| 88 | </tr> |
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| 89 | |
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| 90 | <tr> |
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| 91 | <td valign="top">Const reference type</td> |
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| 92 | |
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| 93 | <td valign="top"><tt>X::const_reference</tt></td> |
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| 94 | |
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| 95 | <td valign="top">A type that behaves like a const reference to the |
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| 96 | Collection's value type.</td> |
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| 97 | </tr> |
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| 98 | |
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| 99 | <tr> |
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| 100 | <td valign="top">Pointer type</td> |
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| 101 | |
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| 102 | <td valign="top"><tt>X::pointer</tt></td> |
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| 103 | |
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| 104 | <td valign="top">A type that behaves as a pointer to the Collection's |
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| 105 | value type.</td> |
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| 106 | </tr> |
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| 107 | |
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| 108 | <tr> |
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| 109 | <td valign="top">Distance type</td> |
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| 110 | |
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| 111 | <td valign="top"><tt>X::difference_type</tt></td> |
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| 112 | |
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| 113 | <td valign="top">A signed integral type used to represent the distance |
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| 114 | between two of the Collection's iterators. This type must be the same |
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| 115 | as the iterator's distance type.</td> |
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| 116 | </tr> |
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| 117 | |
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| 118 | <tr> |
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| 119 | <td valign="top">Size type</td> |
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| 120 | |
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| 121 | <td valign="top"><tt>X::size_type</tt></td> |
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| 122 | |
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| 123 | <td valign="top">An unsigned integral type that can represent any |
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| 124 | nonnegative value of the Collection's distance type.</td> |
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| 125 | </tr> |
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| 126 | </table> |
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| 127 | |
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| 128 | <h3>Notation</h3> |
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| 129 | |
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| 130 | <table summary=""> |
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| 131 | <tr> |
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| 132 | <td valign="top"><tt>X</tt></td> |
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| 133 | |
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| 134 | <td valign="top">A type that is a model of Collection.</td> |
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| 135 | </tr> |
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| 136 | |
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| 137 | <tr> |
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| 138 | <td valign="top"><tt>a</tt>, <tt>b</tt></td> |
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| 139 | |
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| 140 | <td valign="top">Object of type <tt>X</tt>.</td> |
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| 141 | </tr> |
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| 142 | |
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| 143 | <tr> |
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| 144 | <td valign="top"><tt>T</tt></td> |
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| 145 | |
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| 146 | <td valign="top">The value type of <tt>X</tt>.</td> |
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| 147 | </tr> |
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| 148 | </table> |
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| 149 | |
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| 150 | <h3>Valid expressions</h3> |
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| 151 | |
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| 152 | <p>The following expressions must be valid.</p> |
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| 153 | |
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| 154 | <table border summary=""> |
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| 155 | <tr> |
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| 156 | <th>Name</th> |
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| 157 | |
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| 158 | <th>Expression</th> |
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| 159 | |
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| 160 | <th>Return type</th> |
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| 161 | </tr> |
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| 162 | |
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| 163 | <tr> |
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| 164 | <td valign="top">Beginning of range</td> |
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| 165 | |
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| 166 | <td valign="top"><tt>a.begin()</tt></td> |
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| 167 | |
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| 168 | <td valign="top"><tt>iterator</tt> if <tt>a</tt> is mutable, |
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| 169 | <tt>const_iterator</tt> otherwise</td> |
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| 170 | </tr> |
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| 171 | |
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| 172 | <tr> |
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| 173 | <td valign="top">End of range</td> |
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| 174 | |
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| 175 | <td valign="top"><tt>a.end()</tt></td> |
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| 176 | |
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| 177 | <td valign="top"><tt>iterator</tt> if <tt>a</tt> is mutable, |
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| 178 | <tt>const_iterator</tt> otherwise</td> |
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| 179 | </tr> |
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| 180 | |
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| 181 | <tr> |
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| 182 | <td valign="top">Size</td> |
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| 183 | |
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| 184 | <td valign="top"><tt>a.size()</tt></td> |
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| 185 | |
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| 186 | <td valign="top"><tt>size_type</tt></td> |
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| 187 | </tr><!-- |
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| 188 | <TR> |
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| 189 | <TD VAlign=top> |
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| 190 | Maximum size |
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| 191 | </TD> |
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| 192 | <TD VAlign=top> |
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| 193 | <tt>a.max_size()</tt> |
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| 194 | </TD> |
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| 195 | <TD VAlign=top> |
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| 196 | <tt>size_type</tt> |
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| 197 | </TD> |
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| 198 | </TR> |
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| 199 | --> |
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| 200 | |
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| 201 | <tr> |
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| 202 | <td valign="top">Empty Collection</td> |
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| 203 | |
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| 204 | <td valign="top"><tt>a.empty()</tt></td> |
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| 205 | |
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| 206 | <td valign="top">Convertible to <tt>bool</tt></td> |
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| 207 | </tr> |
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| 208 | |
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| 209 | <tr> |
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| 210 | <td valign="top">Swap</td> |
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| 211 | |
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| 212 | <td valign="top"><tt>a.swap(b)</tt></td> |
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| 213 | |
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| 214 | <td valign="top"><tt>void</tt></td> |
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| 215 | </tr> |
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| 216 | </table> |
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| 217 | |
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| 218 | <h3>Expression semantics</h3> |
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| 219 | |
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| 220 | <table border summary=""> |
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| 221 | <tr> |
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| 222 | <th>Name</th> |
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| 223 | |
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| 224 | <th>Expression</th> |
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| 225 | |
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| 226 | <th>Semantics</th> |
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| 227 | |
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| 228 | <th>Postcondition</th> |
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| 229 | </tr> |
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| 230 | |
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| 231 | <tr> |
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| 232 | <td valign="top">Beginning of range</td> |
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| 233 | |
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| 234 | <td valign="top"><tt>a.begin()</tt></td> |
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| 235 | |
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| 236 | <td valign="top">Returns an iterator pointing to the first element in |
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| 237 | the Collection.</td> |
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| 238 | |
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| 239 | <td valign="top"><tt>a.begin()</tt> is either dereferenceable or |
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| 240 | past-the-end. It is past-the-end if and only if <tt>a.size() == |
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| 241 | 0</tt>.</td> |
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| 242 | </tr> |
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| 243 | |
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| 244 | <tr> |
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| 245 | <td valign="top">End of range</td> |
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| 246 | |
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| 247 | <td valign="top"><tt>a.end()</tt></td> |
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| 248 | |
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| 249 | <td valign="top">Returns an iterator pointing one past the last element |
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| 250 | in the Collection.</td> |
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| 251 | |
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| 252 | <td valign="top"><tt>a.end()</tt> is past-the-end.</td> |
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| 253 | </tr> |
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| 254 | |
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| 255 | <tr> |
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| 256 | <td valign="top">Size</td> |
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| 257 | |
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| 258 | <td valign="top"><tt>a.size()</tt></td> |
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| 259 | |
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| 260 | <td valign="top">Returns the size of the Collection, that is, its |
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| 261 | number of elements.</td> |
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| 262 | |
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| 263 | <td valign="top"><tt>a.size() >= 0</tt></td> |
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| 264 | </tr><!-- |
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| 265 | <TR> |
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| 266 | <TD VAlign=top> |
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| 267 | Maximum size |
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| 268 | </TD> |
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| 269 | <TD VAlign=top> |
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| 270 | <tt>a.max_size()</tt> |
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| 271 | </TD> |
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| 272 | <TD VAlign=top> |
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| 273 | |
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| 274 | </TD> |
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| 275 | <TD VAlign=top> |
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| 276 | Returns the largest size that this Collection can ever have. <A href="#8">[8]</A> |
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| 277 | </TD> |
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| 278 | <TD VAlign=top> |
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| 279 | <tt>a.max_size() >= 0 && a.max_size() >= a.size()</tt> |
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| 280 | </TD> |
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| 281 | </TR> |
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| 282 | --> |
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| 283 | |
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| 284 | <tr> |
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| 285 | <td valign="top">Empty Collection</td> |
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| 286 | |
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| 287 | <td valign="top"><tt>a.empty()</tt></td> |
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| 288 | |
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| 289 | <td valign="top">Equivalent to <tt>a.size() == 0</tt>. (But possibly |
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| 290 | faster.)</td> |
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| 291 | |
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| 292 | <td valign="top"> </td> |
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| 293 | </tr> |
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| 294 | |
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| 295 | <tr> |
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| 296 | <td valign="top">Swap</td> |
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| 297 | |
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| 298 | <td valign="top"><tt>a.swap(b)</tt></td> |
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| 299 | |
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| 300 | <td valign="top">Equivalent to <tt>swap(a,b)</tt></td> |
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| 301 | |
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| 302 | <td valign="top"> </td> |
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| 303 | </tr> |
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| 304 | </table> |
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| 305 | |
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| 306 | <h3>Complexity guarantees</h3> |
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| 307 | |
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| 308 | <p><tt>begin()</tt> and <tt>end()</tt> are amortized constant time.</p> |
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| 309 | |
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| 310 | <p><tt>size()</tt> is at most linear in the Collection's size. |
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| 311 | <tt>empty()</tt> is amortized constant time.</p> |
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| 312 | |
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| 313 | <p><tt>swap()</tt> is at most linear in the size of the two |
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| 314 | collections.</p> |
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| 315 | |
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| 316 | <h3>Invariants</h3> |
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| 317 | |
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| 318 | <table border summary=""> |
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| 319 | <tr> |
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| 320 | <td valign="top">Valid range</td> |
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| 321 | |
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| 322 | <td valign="top">For any Collection <tt>a</tt>, <tt>[a.begin(), |
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| 323 | a.end())</tt> is a valid range.</td> |
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| 324 | </tr> |
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| 325 | |
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| 326 | <tr> |
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| 327 | <td valign="top">Range size</td> |
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| 328 | |
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| 329 | <td valign="top"><tt>a.size()</tt> is equal to the distance from |
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| 330 | <tt>a.begin()</tt> to <tt>a.end()</tt>.</td> |
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| 331 | </tr> |
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| 332 | |
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| 333 | <tr> |
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| 334 | <td valign="top">Completeness</td> |
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| 335 | |
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| 336 | <td valign="top">An algorithm that iterates through the range |
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| 337 | <tt>[a.begin(), a.end())</tt> will pass through every element of |
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| 338 | <tt>a</tt>.</td> |
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| 339 | </tr> |
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| 340 | </table> |
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| 341 | |
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| 342 | <h3>Models</h3> |
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| 343 | |
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| 344 | <ul> |
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| 345 | <li><tt>array</tt></li> |
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| 346 | |
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| 347 | <li><tt>array_ptr</tt></li> |
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| 348 | |
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| 349 | <li><tt>vector<bool></tt></li> |
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| 350 | </ul> |
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| 351 | |
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| 352 | <h3>Collection Refinements</h3> |
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| 353 | |
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| 354 | <p>There are quite a few concepts that refine the Collection concept, |
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| 355 | similar to the concepts that refine the Container concept. Here is a brief |
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| 356 | overview of the refining concepts.</p> |
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| 357 | |
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| 358 | <h4>ForwardCollection</h4> |
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| 359 | |
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| 360 | <p>The elements are arranged in some order that does not change |
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| 361 | spontaneously from one iteration to the next. As a result, a |
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| 362 | ForwardCollection is <a href= |
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| 363 | "http://www.sgi.com/tech/stl/EqualityComparable.html">EqualityComparable</a> |
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| 364 | and <a href= |
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| 365 | "http://www.sgi.com/tech/stl/LessThanComparable.html">LessThanComparable</a>. |
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| 366 | In addition, the iterator type of a ForwardCollection is a |
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| 367 | MultiPassInputIterator which is just an InputIterator with the added |
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| 368 | requirements that the iterator can be used to make multiple passes through |
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| 369 | a range, and that if <tt>it1 == it2</tt> and <tt>it1</tt> is |
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| 370 | dereferenceable then <tt>++it1 == ++it2</tt>. The ForwardCollection also |
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| 371 | has a <tt>front()</tt> method.</p> |
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| 372 | |
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| 373 | <table border summary=""> |
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| 374 | <tr> |
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| 375 | <th>Name</th> |
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| 376 | |
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| 377 | <th>Expression</th> |
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| 378 | |
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| 379 | <th>Return type</th> |
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| 380 | |
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| 381 | <th>Semantics</th> |
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| 382 | </tr> |
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| 383 | |
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| 384 | <tr> |
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| 385 | <td valign="top">Front</td> |
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| 386 | |
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| 387 | <td valign="top"><tt>a.front()</tt></td> |
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| 388 | |
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| 389 | <td valign="top"><tt>reference</tt> if <tt>a</tt> is mutable,<br> |
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| 390 | <tt>const_reference</tt> otherwise.</td> |
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| 391 | |
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| 392 | <td valign="top">Equivalent to <tt>*(a.begin())</tt>.</td> |
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| 393 | </tr> |
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| 394 | </table> |
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| 395 | |
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| 396 | <h4>ReversibleCollection</h4> |
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| 397 | |
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| 398 | <p>The container provides access to iterators that traverse in both |
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| 399 | directions (forward and reverse). The iterator type must meet all of the |
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| 400 | requirements of <a href= |
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| 401 | "http://www.sgi.com/tech/stl/BidirectionalIterator.html">BidirectionalIterator</a> |
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| 402 | except that the reference type does not have to be a real C++ reference. |
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| 403 | The ReversibleCollection adds the following requirements to those of |
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| 404 | ForwardCollection.</p> |
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| 405 | |
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| 406 | <table border summary=""> |
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| 407 | <tr> |
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| 408 | <th>Name</th> |
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| 409 | |
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| 410 | <th>Expression</th> |
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| 411 | |
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| 412 | <th>Return type</th> |
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| 413 | |
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| 414 | <th>Semantics</th> |
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| 415 | </tr> |
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| 416 | |
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| 417 | <tr> |
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| 418 | <td valign="top">Beginning of range</td> |
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| 419 | |
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| 420 | <td valign="top"><tt>a.rbegin()</tt></td> |
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| 421 | |
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| 422 | <td valign="top"><tt>reverse_iterator</tt> if <tt>a</tt> is mutable, |
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| 423 | <tt>const_reverse_iterator</tt> otherwise.</td> |
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| 424 | |
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| 425 | <td valign="top">Equivalent to |
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| 426 | <tt>X::reverse_iterator(a.end())</tt>.</td> |
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| 427 | </tr> |
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| 428 | |
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| 429 | <tr> |
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| 430 | <td valign="top">End of range</td> |
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| 431 | |
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| 432 | <td valign="top"><tt>a.rend()</tt></td> |
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| 433 | |
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| 434 | <td valign="top"><tt>reverse_iterator</tt> if <tt>a</tt> is mutable, |
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| 435 | <tt>const_reverse_iterator</tt> otherwise.</td> |
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| 436 | |
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| 437 | <td valign="top">Equivalent to |
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| 438 | <tt>X::reverse_iterator(a.begin())</tt>.</td> |
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| 439 | </tr> |
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| 440 | |
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| 441 | <tr> |
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| 442 | <td valign="top">Back</td> |
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| 443 | |
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| 444 | <td valign="top"><tt>a.back()</tt></td> |
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| 445 | |
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| 446 | <td valign="top"><tt>reference</tt> if <tt>a</tt> is mutable,<br> |
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| 447 | <tt>const_reference</tt> otherwise.</td> |
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| 448 | |
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| 449 | <td valign="top">Equivalent to <tt>*(--a.end())</tt>.</td> |
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| 450 | </tr> |
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| 451 | </table> |
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| 452 | |
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| 453 | <h4>SequentialCollection</h4> |
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| 454 | |
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| 455 | <p>The elements are arranged in a strict linear order. No extra methods are |
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| 456 | required.</p> |
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| 457 | |
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| 458 | <h4>RandomAccessCollection</h4> |
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| 459 | |
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| 460 | <p>The iterators of a RandomAccessCollection satisfy all of the |
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| 461 | requirements of <a href= |
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| 462 | "http://www.sgi.com/tech/stl/RandomAccessIterator.html">RandomAccessIterator</a> |
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| 463 | except that the reference type does not have to be a real C++ reference. In |
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| 464 | addition, a RandomAccessCollection provides an element access operator.</p> |
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| 465 | |
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| 466 | <table border summary=""> |
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| 467 | <tr> |
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| 468 | <th>Name</th> |
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| 469 | |
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| 470 | <th>Expression</th> |
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| 471 | |
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| 472 | <th>Return type</th> |
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| 473 | |
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| 474 | <th>Semantics</th> |
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| 475 | </tr> |
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| 476 | |
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| 477 | <tr> |
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| 478 | <td valign="top">Element Access</td> |
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| 479 | |
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| 480 | <td valign="top"><tt>a[n]</tt></td> |
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| 481 | |
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| 482 | <td valign="top"><tt>reference</tt> if <tt>a</tt> is mutable, |
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| 483 | <tt>const_reference</tt> otherwise.</td> |
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| 484 | |
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| 485 | <td valign="top">Returns the nth element of the Collection. <tt>n</tt> |
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| 486 | must be convertible to <tt>size_type</tt>. Precondition: <tt>0 <= n |
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| 487 | < a.size()</tt>.</td> |
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| 488 | </tr> |
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| 489 | </table> |
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| 490 | |
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| 491 | <h3>Notes</h3> |
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| 492 | |
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| 493 | <p><a name="n1" id="n1">[1]</a> The reference type does not have to be a |
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| 494 | real C++ reference. The requirements of the reference type depend on the |
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| 495 | context within which the Collection is being used. Specifically it depends |
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| 496 | on the requirements the context places on the value type of the Collection. |
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| 497 | The reference type of the Collection must meet the same requirements as the |
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| 498 | value type. In addition, the reference objects must be equivalent to the |
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| 499 | value type objects in the collection (which is trivially true if they are |
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| 500 | the same object). Also, in a mutable Collection, an assignment to the |
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| 501 | reference object must result in an assignment to the object in the |
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| 502 | Collection (again, which is trivially true if they are the same object, but |
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| 503 | non-trivial if the reference type is a proxy class).</p> |
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| 504 | |
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| 505 | <h3>See also</h3> |
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| 506 | |
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| 507 | <p><a href= |
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| 508 | "http://www.sgi.com/tech/stl/Container.html">Container</a><br></p> |
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| 509 | <hr> |
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| 510 | |
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| 511 | <p><a href="http://validator.w3.org/check?uri=referer"><img border="0" src= |
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| 512 | "http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01 Transitional" |
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| 513 | height="31" width="88"></a></p> |
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| 514 | |
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| 515 | <p>Revised |
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| 516 | <!--webbot bot="Timestamp" s-type="EDITED" s-format="%d %B, %Y" startspan -->05 |
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| 517 | December, 2006<!--webbot bot="Timestamp" endspan i-checksum="38516" --></p> |
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| 518 | |
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| 519 | <table summary=""> |
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| 520 | <tr valign="top"> |
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| 521 | <td nowrap><i>Copyright © 2000</i></td> |
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| 522 | |
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| 523 | <td><i><a href="http://www.boost.org/people/jeremy_siek.htm">Jeremy |
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| 524 | Siek</a>, Univ.of Notre Dame and C++ Library & Compiler Group/SGI |
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| 525 | (<a href="mailto:jsiek@engr.sgi.com">jsiek@engr.sgi.com</a>)</i></td> |
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| 526 | </tr> |
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| 527 | </table> |
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| 528 | |
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| 529 | <p><i>Distributed under the Boost Software License, Version 1.0. (See |
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| 530 | accompanying file <a href="../../LICENSE_1_0.txt">LICENSE_1_0.txt</a> or |
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| 531 | copy at <a href= |
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| 532 | "http://www.boost.org/LICENSE_1_0.txt">http://www.boost.org/LICENSE_1_0.txt</a>)</i></p> |
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| 533 | </body> |
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| 534 | </html> |
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