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535 lines
15 KiB
HTML
535 lines
15 KiB
HTML
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<html>
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<head>
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<meta http-equiv="Content-Language" content="en-us">
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<meta http-equiv="Content-Type" content="text/html; charset=us-ascii">
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<title>Collection</title>
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</head>
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<body bgcolor="#FFFFFF" link="#0000EE" text="#000000" vlink="#551A8B" alink=
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"#FF0000">
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<h1><img src="../../boost.png" alt="boost logo" width="277" align="middle"
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height="86"><br>
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Collection</h1>
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<h3>Description</h3>
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<p>A Collection is a <i>concept</i> similar to the STL <a href=
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"http://www.sgi.com/tech/stl/Container.html">Container</a> concept. A
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Collection provides iterators for accessing a range of elements and
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provides information about the number of elements in the Collection.
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However, a Collection has fewer requirements than a Container. The
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motivation for the Collection concept is that there are many useful
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Container-like types that do not meet the full requirements of Container,
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and many algorithms that can be written with this reduced set of
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requirements. To summarize the reduction in requirements:</p>
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<ul>
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<li>It is not required to "own" its elements: the lifetime of an element
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in a Collection does not have to match the lifetime of the Collection
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object, though the lifetime of the element should cover the lifetime of
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the Collection object.</li>
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<li>The semantics of copying a Collection object is not defined (it could
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be a deep or shallow copy or not even support copying).</li>
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<li>The associated reference type of a Collection does not have to be a
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real C++ reference.</li>
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</ul>Because of the reduced requirements, some care must be taken when
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writing code that is meant to be generic for all Collection types. In
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particular, a Collection object should be passed by-reference since
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assumptions can not be made about the behaviour of the copy constructor.
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<h3>Associated types</h3>
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<table border summary="">
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<tr>
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<td valign="top">Value type</td>
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<td valign="top"><tt>X::value_type</tt></td>
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<td valign="top">The type of the object stored in a Collection. If the
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Collection is <i>mutable</i> then the value type must be <a href=
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"http://www.sgi.com/tech/stl/Assignable.html">Assignable</a>. Otherwise
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the value type must be <a href=
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"./CopyConstructible.html">CopyConstructible</a>.</td>
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</tr>
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<tr>
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<td valign="top">Iterator type</td>
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<td valign="top"><tt>X::iterator</tt></td>
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<td valign="top">The type of iterator used to iterate through a
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Collection's elements. The iterator's value type is expected to be the
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Collection's value type. A conversion from the iterator type to the
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const iterator type must exist. The iterator type must be an <a href=
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"http://www.sgi.com/tech/stl/InputIterator.html">InputIterator</a>.</td>
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</tr>
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<tr>
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<td valign="top">Const iterator type</td>
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<td valign="top"><tt>X::const_iterator</tt></td>
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<td valign="top">A type of iterator that may be used to examine, but
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not to modify, a Collection's elements.</td>
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</tr>
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<tr>
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<td valign="top">Reference type</td>
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<td valign="top"><tt>X::reference</tt></td>
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<td valign="top">A type that behaves like a reference to the
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Collection's value type. <a href="#n1">[1]</a></td>
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</tr>
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<tr>
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<td valign="top">Const reference type</td>
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<td valign="top"><tt>X::const_reference</tt></td>
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<td valign="top">A type that behaves like a const reference to the
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Collection's value type.</td>
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</tr>
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<tr>
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<td valign="top">Pointer type</td>
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<td valign="top"><tt>X::pointer</tt></td>
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<td valign="top">A type that behaves as a pointer to the Collection's
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value type.</td>
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</tr>
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<tr>
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<td valign="top">Distance type</td>
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<td valign="top"><tt>X::difference_type</tt></td>
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<td valign="top">A signed integral type used to represent the distance
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between two of the Collection's iterators. This type must be the same
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as the iterator's distance type.</td>
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</tr>
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<tr>
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<td valign="top">Size type</td>
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<td valign="top"><tt>X::size_type</tt></td>
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<td valign="top">An unsigned integral type that can represent any
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nonnegative value of the Collection's distance type.</td>
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</tr>
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</table>
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<h3>Notation</h3>
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<table summary="">
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<tr>
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<td valign="top"><tt>X</tt></td>
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<td valign="top">A type that is a model of Collection.</td>
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</tr>
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<tr>
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<td valign="top"><tt>a</tt>, <tt>b</tt></td>
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<td valign="top">Object of type <tt>X</tt>.</td>
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</tr>
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<tr>
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<td valign="top"><tt>T</tt></td>
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<td valign="top">The value type of <tt>X</tt>.</td>
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</tr>
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</table>
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<h3>Valid expressions</h3>
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<p>The following expressions must be valid.</p>
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<table border summary="">
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<tr>
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<th>Name</th>
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<th>Expression</th>
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<th>Return type</th>
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</tr>
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<tr>
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<td valign="top">Beginning of range</td>
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<td valign="top"><tt>a.begin()</tt></td>
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<td valign="top"><tt>iterator</tt> if <tt>a</tt> is mutable,
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<tt>const_iterator</tt> otherwise</td>
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</tr>
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<tr>
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<td valign="top">End of range</td>
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<td valign="top"><tt>a.end()</tt></td>
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<td valign="top"><tt>iterator</tt> if <tt>a</tt> is mutable,
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<tt>const_iterator</tt> otherwise</td>
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</tr>
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<tr>
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<td valign="top">Size</td>
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<td valign="top"><tt>a.size()</tt></td>
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<td valign="top"><tt>size_type</tt></td>
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</tr><!--
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<TR>
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<TD VAlign=top>
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Maximum size
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</TD>
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<TD VAlign=top>
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<tt>a.max_size()</tt>
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</TD>
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<TD VAlign=top>
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<tt>size_type</tt>
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</TD>
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</TR>
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-->
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<tr>
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<td valign="top">Empty Collection</td>
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<td valign="top"><tt>a.empty()</tt></td>
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<td valign="top">Convertible to <tt>bool</tt></td>
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</tr>
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<tr>
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<td valign="top">Swap</td>
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<td valign="top"><tt>a.swap(b)</tt></td>
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<td valign="top"><tt>void</tt></td>
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</tr>
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</table>
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<h3>Expression semantics</h3>
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<table border summary="">
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<tr>
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<th>Name</th>
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<th>Expression</th>
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<th>Semantics</th>
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<th>Postcondition</th>
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</tr>
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<tr>
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<td valign="top">Beginning of range</td>
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<td valign="top"><tt>a.begin()</tt></td>
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<td valign="top">Returns an iterator pointing to the first element in
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the Collection.</td>
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<td valign="top"><tt>a.begin()</tt> is either dereferenceable or
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past-the-end. It is past-the-end if and only if <tt>a.size() ==
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0</tt>.</td>
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</tr>
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<tr>
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<td valign="top">End of range</td>
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<td valign="top"><tt>a.end()</tt></td>
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<td valign="top">Returns an iterator pointing one past the last element
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in the Collection.</td>
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<td valign="top"><tt>a.end()</tt> is past-the-end.</td>
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</tr>
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<tr>
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<td valign="top">Size</td>
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<td valign="top"><tt>a.size()</tt></td>
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<td valign="top">Returns the size of the Collection, that is, its
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number of elements.</td>
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<td valign="top"><tt>a.size() >= 0</tt></td>
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</tr><!--
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<TR>
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<TD VAlign=top>
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Maximum size
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</TD>
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<TD VAlign=top>
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<tt>a.max_size()</tt>
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</TD>
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<TD VAlign=top>
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</TD>
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<TD VAlign=top>
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Returns the largest size that this Collection can ever have. <A href="#8">[8]</A>
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</TD>
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<TD VAlign=top>
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<tt>a.max_size() >= 0 && a.max_size() >= a.size()</tt>
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</TD>
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</TR>
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-->
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<tr>
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<td valign="top">Empty Collection</td>
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<td valign="top"><tt>a.empty()</tt></td>
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<td valign="top">Equivalent to <tt>a.size() == 0</tt>. (But possibly
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faster.)</td>
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<td valign="top"> </td>
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</tr>
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<tr>
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<td valign="top">Swap</td>
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<td valign="top"><tt>a.swap(b)</tt></td>
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<td valign="top">Equivalent to <tt>swap(a,b)</tt></td>
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<td valign="top"> </td>
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</tr>
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</table>
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<h3>Complexity guarantees</h3>
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<p><tt>begin()</tt> and <tt>end()</tt> are amortized constant time.</p>
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<p><tt>size()</tt> is at most linear in the Collection's size.
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<tt>empty()</tt> is amortized constant time.</p>
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<p><tt>swap()</tt> is at most linear in the size of the two
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collections.</p>
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<h3>Invariants</h3>
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<table border summary="">
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<tr>
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<td valign="top">Valid range</td>
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<td valign="top">For any Collection <tt>a</tt>, <tt>[a.begin(),
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a.end())</tt> is a valid range.</td>
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</tr>
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<tr>
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<td valign="top">Range size</td>
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<td valign="top"><tt>a.size()</tt> is equal to the distance from
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<tt>a.begin()</tt> to <tt>a.end()</tt>.</td>
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</tr>
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<tr>
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<td valign="top">Completeness</td>
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<td valign="top">An algorithm that iterates through the range
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<tt>[a.begin(), a.end())</tt> will pass through every element of
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<tt>a</tt>.</td>
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</tr>
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</table>
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<h3>Models</h3>
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<ul>
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<li><tt>array</tt></li>
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<li><tt>array_ptr</tt></li>
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<li><tt>vector<bool></tt></li>
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</ul>
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<h3>Collection Refinements</h3>
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<p>There are quite a few concepts that refine the Collection concept,
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similar to the concepts that refine the Container concept. Here is a brief
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overview of the refining concepts.</p>
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<h4>ForwardCollection</h4>
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<p>The elements are arranged in some order that does not change
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spontaneously from one iteration to the next. As a result, a
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ForwardCollection is <a href=
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"http://www.sgi.com/tech/stl/EqualityComparable.html">EqualityComparable</a>
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and <a href=
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"http://www.sgi.com/tech/stl/LessThanComparable.html">LessThanComparable</a>.
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In addition, the iterator type of a ForwardCollection is a
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MultiPassInputIterator which is just an InputIterator with the added
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requirements that the iterator can be used to make multiple passes through
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a range, and that if <tt>it1 == it2</tt> and <tt>it1</tt> is
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dereferenceable then <tt>++it1 == ++it2</tt>. The ForwardCollection also
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has a <tt>front()</tt> method.</p>
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<table border summary="">
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<tr>
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<th>Name</th>
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<th>Expression</th>
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<th>Return type</th>
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<th>Semantics</th>
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</tr>
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<tr>
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<td valign="top">Front</td>
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<td valign="top"><tt>a.front()</tt></td>
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<td valign="top"><tt>reference</tt> if <tt>a</tt> is mutable,<br>
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<tt>const_reference</tt> otherwise.</td>
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<td valign="top">Equivalent to <tt>*(a.begin())</tt>.</td>
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</tr>
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</table>
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<h4>ReversibleCollection</h4>
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<p>The container provides access to iterators that traverse in both
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directions (forward and reverse). The iterator type must meet all of the
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requirements of <a href=
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"http://www.sgi.com/tech/stl/BidirectionalIterator.html">BidirectionalIterator</a>
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except that the reference type does not have to be a real C++ reference.
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The ReversibleCollection adds the following requirements to those of
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ForwardCollection.</p>
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<table border summary="">
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<tr>
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<th>Name</th>
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<th>Expression</th>
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<th>Return type</th>
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<th>Semantics</th>
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</tr>
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<tr>
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<td valign="top">Beginning of range</td>
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<td valign="top"><tt>a.rbegin()</tt></td>
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<td valign="top"><tt>reverse_iterator</tt> if <tt>a</tt> is mutable,
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<tt>const_reverse_iterator</tt> otherwise.</td>
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<td valign="top">Equivalent to
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<tt>X::reverse_iterator(a.end())</tt>.</td>
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</tr>
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<tr>
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<td valign="top">End of range</td>
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<td valign="top"><tt>a.rend()</tt></td>
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<td valign="top"><tt>reverse_iterator</tt> if <tt>a</tt> is mutable,
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<tt>const_reverse_iterator</tt> otherwise.</td>
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<td valign="top">Equivalent to
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<tt>X::reverse_iterator(a.begin())</tt>.</td>
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</tr>
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<tr>
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<td valign="top">Back</td>
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<td valign="top"><tt>a.back()</tt></td>
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<td valign="top"><tt>reference</tt> if <tt>a</tt> is mutable,<br>
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<tt>const_reference</tt> otherwise.</td>
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<td valign="top">Equivalent to <tt>*(--a.end())</tt>.</td>
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</tr>
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</table>
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<h4>SequentialCollection</h4>
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<p>The elements are arranged in a strict linear order. No extra methods are
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required.</p>
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<h4>RandomAccessCollection</h4>
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<p>The iterators of a RandomAccessCollection satisfy all of the
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requirements of <a href=
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"http://www.sgi.com/tech/stl/RandomAccessIterator.html">RandomAccessIterator</a>
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except that the reference type does not have to be a real C++ reference. In
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addition, a RandomAccessCollection provides an element access operator.</p>
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<table border summary="">
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<tr>
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<th>Name</th>
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<th>Expression</th>
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<th>Return type</th>
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<th>Semantics</th>
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</tr>
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<tr>
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<td valign="top">Element Access</td>
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<td valign="top"><tt>a[n]</tt></td>
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<td valign="top"><tt>reference</tt> if <tt>a</tt> is mutable,
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<tt>const_reference</tt> otherwise.</td>
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<td valign="top">Returns the nth element of the Collection. <tt>n</tt>
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must be convertible to <tt>size_type</tt>. Precondition: <tt>0 <= n
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< a.size()</tt>.</td>
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</tr>
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</table>
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<h3>Notes</h3>
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<p><a name="n1" id="n1">[1]</a> The reference type does not have to be a
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real C++ reference. The requirements of the reference type depend on the
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context within which the Collection is being used. Specifically it depends
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on the requirements the context places on the value type of the Collection.
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The reference type of the Collection must meet the same requirements as the
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value type. In addition, the reference objects must be equivalent to the
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value type objects in the collection (which is trivially true if they are
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the same object). Also, in a mutable Collection, an assignment to the
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reference object must result in an assignment to the object in the
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Collection (again, which is trivially true if they are the same object, but
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non-trivial if the reference type is a proxy class).</p>
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<h3>See also</h3>
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<p><a href=
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"http://www.sgi.com/tech/stl/Container.html">Container</a><br></p>
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<hr>
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<p><a href="http://validator.w3.org/check?uri=referer"><img border="0" src=
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"../../doc/images/valid-html401.png" alt="Valid HTML 4.01 Transitional"
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height="31" width="88"></a></p>
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<p>Revised
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<!--webbot bot="Timestamp" s-type="EDITED" s-format="%d %B, %Y" startspan -->05
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December, 2006<!--webbot bot="Timestamp" endspan i-checksum="38516" --></p>
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<table summary="">
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<tr valign="top">
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<td nowrap><i>Copyright © 2000</i></td>
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<td><i><a href="http://www.boost.org/people/jeremy_siek.htm">Jeremy
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Siek</a>, Univ.of Notre Dame and C++ Library & Compiler Group/SGI
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(<a href="mailto:jsiek@engr.sgi.com">jsiek@engr.sgi.com</a>)</i></td>
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</tr>
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</table>
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<p><i>Distributed under the Boost Software License, Version 1.0. (See
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accompanying file <a href="../../LICENSE_1_0.txt">LICENSE_1_0.txt</a> or
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copy at <a href=
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"http://www.boost.org/LICENSE_1_0.txt">http://www.boost.org/LICENSE_1_0.txt</a>)</i></p>
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