e755a0fafb
- Better support for attributes on root elements - including `lang`. - Add missing copyright to some files. [SVN r67666]
554 lines
22 KiB
XML
554 lines
22 KiB
XML
<?xml version="1.0" encoding="utf-8"?>
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<!--
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Copyright 2010 Daniel James.
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Distributed under the Boost Software License, Version 1.0.
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(See accompanying file LICENSE_1_0.txt or copy at
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http://www.boost.org/LICENSE_1_0.txt)
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-->
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<!DOCTYPE library PUBLIC "-//Boost//DTD BoostBook XML V1.0//EN"
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"http://www.boost.org/tools/boostbook/dtd/boostbook.dtd">
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<library name="Array" dirname="array" id="array" last-revision="$Date$">
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<libraryinfo>
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<author>
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<firstname>Nicolai</firstname>
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<surname>Josuttis</surname>
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</author>
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<copyright>
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<year>2001</year>
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<year>2002</year>
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<year>2003</year>
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<year>2004</year>
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<holder>Nicolai M. Josuttis</holder>
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</copyright>
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<legalnotice>
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<para>Distributed under the Boost Software License, Version 1.0.
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(See accompanying file <filename>LICENSE_1_0.txt</filename> or copy at
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<ulink
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url="http://www.boost.org/LICENSE_1_0.txt">http://www.boost.org/LICENSE_1_0.txt</ulink>)
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</para>
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</legalnotice>
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<librarypurpose>STL compliant container wrapper for arrays of constant size</librarypurpose>
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<librarycategory name="category:containers"/>
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</libraryinfo>
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<title>Boost.Array</title>
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<section id="array.intro">
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<title>Introduction</title>
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<using-namespace name="boost"/>
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<using-class name="array"/>
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<para>The C++ Standard Template Library STL as part of the C++
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Standard Library provides a framework for processing algorithms on
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different kind of containers. However, ordinary arrays don't
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provide the interface of STL containers (although, they provide
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the iterator interface of STL containers).</para>
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<para>As replacement for ordinary arrays, the STL provides class
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<code><classname>std::vector</classname></code>. However,
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<code><classname>std::vector<></classname></code> provides
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the semantics of dynamic arrays. Thus, it manages data to be able
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to change the number of elements. This results in some overhead in
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case only arrays with static size are needed.</para>
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<para>In his book, <emphasis>Generic Programming and the
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STL</emphasis>, Matthew H. Austern introduces a useful wrapper
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class for ordinary arrays with static size, called
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<code>block</code>. It is safer and has no worse performance than
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ordinary arrays. In <emphasis>The C++ Programming
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Language</emphasis>, 3rd edition, Bjarne Stroustrup introduces a
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similar class, called <code>c_array</code>, which I (<ulink
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url="http://www.josuttis.com">Nicolai Josuttis</ulink>) present
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slightly modified in my book <emphasis>The C++ Standard Library -
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A Tutorial and Reference</emphasis>, called
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<code>carray</code>. This is the essence of these approaches
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spiced with many feedback from <ulink
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url="http://www.boost.org">boost</ulink>.</para>
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<para>After considering different names, we decided to name this
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class simply <code><classname>array</classname></code>.</para>
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<para>Note that this class is suggested to be part of the next
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Technical Report, which will extend the C++ Standard (see
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<ulink url="http://std.dkuug.dk/jtc1/sc22/wg21/docs/papers/2003/n1548.htm">http://std.dkuug.dk/jtc1/sc22/wg21/docs/papers/2003/n1548.htm</ulink>).</para>
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<para>Class <code><classname>array</classname></code> fulfills most
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but not all of the requirements of "reversible containers" (see
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Section 23.1, [lib.container.requirements] of the C++
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Standard). The reasons array is not an reversible STL container is
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because:
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<itemizedlist spacing="compact">
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<listitem><simpara>No constructors are provided.</simpara></listitem>
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<listitem><simpara>Elements may have an undetermined initial value (see <xref linkend="array.rationale"/>).</simpara></listitem>
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<listitem><simpara><functionname>swap</functionname>() has no constant complexity.</simpara></listitem>
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<listitem><simpara><methodname>size</methodname>() is always constant, based on the second template argument of the type.</simpara></listitem>
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<listitem><simpara>The container provides no allocator support.</simpara></listitem>
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</itemizedlist>
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</para>
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<para>It doesn't fulfill the requirements of a "sequence" (see Section 23.1.1, [lib.sequence.reqmts] of the C++ Standard), except that:
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<itemizedlist spacing="compact">
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<listitem><simpara><methodname>front</methodname>() and <methodname>back</methodname>() are provided.</simpara></listitem>
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<listitem><simpara><methodname>operator[]</methodname> and <methodname>at</methodname>() are provided.</simpara></listitem>
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</itemizedlist>
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</para>
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</section>
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<library-reference>
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<header name="boost/array.hpp">
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<namespace name="boost">
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<class name="array">
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<template>
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<template-type-parameter name="T"/>
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<template-nontype-parameter name="N">
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<type>std::size_t</type>
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</template-nontype-parameter>
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</template>
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<purpose><para>STL compliant container wrapper for arrays of constant size</para></purpose>
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<typedef name="value_type">
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<type>T</type>
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</typedef>
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<typedef name="iterator">
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<type>T*</type>
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</typedef>
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<typedef name="const_iterator">
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<type>const T*</type>
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</typedef>
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<typedef name="reverse_iterator">
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<type><classname>std::reverse_iterator</classname><iterator></type>
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</typedef>
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<typedef name="const_reverse_iterator">
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<type><classname>std::reverse_iterator</classname><const_iterator></type>
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</typedef>
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<typedef name="reference">
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<type>T&</type>
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</typedef>
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<typedef name="const_reference">
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<type>const T&</type>
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</typedef>
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<typedef name="size_type">
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<type>std::size_t</type>
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</typedef>
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<typedef name="difference_type">
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<type>std::ptrdiff_t</type>
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</typedef>
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<static-constant name="static_size">
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<type>size_type</type>
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<default>N</default>
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</static-constant>
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<copy-assignment>
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<template>
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<template-type-parameter name="U"/>
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</template>
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<parameter name="other">
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<paramtype>const <classname>array</classname><U, N>&</paramtype>
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</parameter>
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<effects><simpara><code>std::copy(rhs.<methodname>begin</methodname>(),rhs.<methodname>end</methodname>(), <methodname>begin</methodname>())</code></simpara></effects>
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</copy-assignment>
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<method-group name="iterator support">
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<overloaded-method name="begin">
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<signature>
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<type>iterator</type>
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</signature>
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<signature cv="const">
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<type>const_iterator</type>
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</signature>
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<returns><simpara>iterator for the first element</simpara></returns>
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<throws><simpara>will not throw</simpara></throws>
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</overloaded-method>
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<overloaded-method name="end">
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<signature>
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<type>iterator</type>
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</signature>
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<signature cv="const">
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<type>const_iterator</type>
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</signature>
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<returns><simpara>iterator for position after the last element</simpara></returns>
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<throws><simpara>will not throw</simpara></throws>
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</overloaded-method>
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</method-group>
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<method-group name="reverse iterator support">
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<overloaded-method name="rbegin">
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<signature>
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<type>reverse_iterator</type>
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</signature>
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<signature cv="const">
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<type>const_reverse_iterator</type>
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</signature>
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<returns><simpara>reverse iterator for the first element of reverse iteration</simpara></returns>
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</overloaded-method>
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<overloaded-method name="rend">
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<signature>
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<type>reverse_iterator</type>
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</signature>
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<signature cv="const">
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<type>const_reverse_iterator</type>
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</signature>
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<returns><simpara>reverse iterator for position after the last element in reverse iteration</simpara></returns>
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</overloaded-method>
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</method-group>
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<method-group name="capacity">
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<method name="size">
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<type>size_type</type>
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<returns><simpara><code>N</code></simpara></returns>
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</method>
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<method name="empty">
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<type>bool</type>
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<returns><simpara><code>N==0</code></simpara></returns>
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<throws><simpara>will not throw</simpara></throws>
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</method>
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<method name="max_size">
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<type>size_type</type>
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<returns><simpara><code>N</code></simpara></returns>
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<throws><simpara>will not throw</simpara></throws>
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</method>
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</method-group>
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<method-group name="element access">
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<overloaded-method name="operator[]">
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<signature>
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<type>reference</type>
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<parameter name="i">
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<paramtype>size_type</paramtype>
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</parameter>
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</signature>
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<signature cv="const">
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<type>const_reference</type>
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<parameter name="i">
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<paramtype>size_type</paramtype>
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</parameter>
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</signature>
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<requires><simpara><code>i < N</code></simpara></requires>
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<returns><simpara>element with index <code>i</code></simpara></returns>
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<throws><simpara>will not throw.</simpara></throws>
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</overloaded-method>
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<overloaded-method name="at">
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<signature>
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<type>reference</type>
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<parameter name="i">
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<paramtype>size_type</paramtype>
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</parameter>
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</signature>
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<signature cv="const">
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<type>const_reference</type>
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<parameter name="i">
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<paramtype>size_type</paramtype>
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</parameter>
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</signature>
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<returns><simpara>element with index <code>i</code></simpara></returns>
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<throws><simpara><code><classname>std::range_error</classname></code> if <code>i >= N</code></simpara></throws>
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</overloaded-method>
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<overloaded-method name="front">
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<signature>
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<type>reference</type>
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</signature>
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<signature cv="const">
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<type>const_reference</type>
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</signature>
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<requires><simpara><code>N > 0</code></simpara></requires>
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<returns><simpara>the first element</simpara></returns>
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<throws><simpara>will not throw</simpara></throws>
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</overloaded-method>
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<overloaded-method name="back">
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<signature>
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<type>reference</type>
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</signature>
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<signature cv="const">
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<type>const_reference</type>
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</signature>
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<requires><simpara><code>N > 0</code></simpara></requires>
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<returns><simpara>the last element</simpara></returns>
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<throws><simpara>will not throw</simpara></throws>
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</overloaded-method>
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<method name="data" cv="const">
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<type>const T*</type>
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<returns><simpara><code>elems</code></simpara></returns>
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<throws><simpara>will not throw</simpara></throws>
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</method>
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<method name="c_array">
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<type>T*</type>
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<returns><simpara><code>elems</code></simpara></returns>
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<throws><simpara>will not throw</simpara></throws>
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</method>
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</method-group>
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<method-group name="modifiers">
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<method name="swap">
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<type>void</type>
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<parameter name="other">
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<paramtype><classname>array</classname><T, N>&</paramtype>
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</parameter>
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<effects><simpara><code>std::swap_ranges(<methodname>begin</methodname>(), <methodname>end</methodname>(), other.<methodname>begin</methodname>())</code></simpara></effects>
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<complexity><simpara>linear in <code>N</code></simpara></complexity>
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</method>
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<method name="assign">
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<type>void</type>
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<parameter name="value">
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<paramtype>const T&</paramtype>
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</parameter>
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<effects><simpara><code>std::fill_n(<methodname>begin</methodname>(), N, value)</code></simpara></effects>
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</method>
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</method-group>
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<data-member name="elems[N]"> <!-- HACK -->
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<type>T</type>
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</data-member>
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<free-function-group name="specialized algorithms">
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<function name="swap">
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<template>
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<template-type-parameter name="T"/>
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<template-nontype-parameter name="N">
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<type>std::size_t</type>
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</template-nontype-parameter>
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</template>
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<type>void</type>
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<parameter name="x">
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<paramtype><classname>array</classname><T, N>&</paramtype>
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</parameter>
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<parameter name="y">
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<paramtype><classname>array</classname><T, N>&</paramtype>
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</parameter>
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<effects><simpara><code>x.<methodname>swap</methodname>(y)</code></simpara></effects>
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<throws><simpara>will not throw.</simpara></throws>
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</function>
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</free-function-group>
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<free-function-group name="comparisons">
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<function name="operator==">
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<template>
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<template-type-parameter name="T"/>
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<template-nontype-parameter name="N">
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<type>std::size_t</type>
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</template-nontype-parameter>
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</template>
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<type>bool</type>
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<parameter name="x">
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<paramtype>const <classname>array</classname><T, N>&</paramtype>
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</parameter>
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<parameter name="y">
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<paramtype>const <classname>array</classname><T, N>&</paramtype>
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</parameter>
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<returns><simpara><code>std::equal(x.<methodname>begin</methodname>(), x.<methodname>end</methodname>(), y.<methodname>begin</methodname>())</code></simpara>
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</returns>
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</function>
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<function name="operator!=">
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<template>
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<template-type-parameter name="T"/>
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<template-nontype-parameter name="N">
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<type>std::size_t</type>
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</template-nontype-parameter>
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</template>
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<type>bool</type>
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<parameter name="x">
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<paramtype>const <classname>array</classname><T, N>&</paramtype>
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</parameter>
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<parameter name="y">
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<paramtype>const <classname>array</classname><T, N>&</paramtype>
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</parameter>
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<returns><simpara><code>!(x == y)</code></simpara>
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</returns>
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</function>
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<function name="operator<">
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<template>
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<template-type-parameter name="T"/>
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<template-nontype-parameter name="N">
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<type>std::size_t</type>
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</template-nontype-parameter>
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</template>
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<type>bool</type>
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<parameter name="x">
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<paramtype>const <classname>array</classname><T, N>&</paramtype>
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</parameter>
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<parameter name="y">
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<paramtype>const <classname>array</classname><T, N>&</paramtype>
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</parameter>
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<returns><simpara><code>std::lexicographical_compare(x.<methodname>begin</methodname>(), x.<methodname>end</methodname>(), y.<methodname>begin</methodname>(), y.<methodname>end</methodname>())</code></simpara>
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</returns>
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</function>
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<function name="operator>">
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<template>
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<template-type-parameter name="T"/>
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<template-nontype-parameter name="N">
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<type>std::size_t</type>
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</template-nontype-parameter>
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</template>
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<type>bool</type>
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<parameter name="x">
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<paramtype>const <classname>array</classname><T, N>&</paramtype>
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</parameter>
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<parameter name="y">
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<paramtype>const <classname>array</classname><T, N>&</paramtype>
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</parameter>
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<returns><simpara><code>y < x</code></simpara></returns>
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</function>
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<function name="operator<=">
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<template>
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<template-type-parameter name="T"/>
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<template-nontype-parameter name="N">
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<type>std::size_t</type>
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</template-nontype-parameter>
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</template>
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<type>bool</type>
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<parameter name="x">
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<paramtype>const <classname>array</classname><T, N>&</paramtype>
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</parameter>
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<parameter name="y">
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<paramtype>const <classname>array</classname><T, N>&</paramtype>
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</parameter>
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<returns><simpara><code>!(y < x)</code></simpara></returns>
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</function>
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<function name="operator>=">
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<template>
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<template-type-parameter name="T"/>
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<template-nontype-parameter name="N">
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<type>std::size_t</type>
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</template-nontype-parameter>
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</template>
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<type>bool</type>
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<parameter name="x">
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<paramtype>const <classname>array</classname><T, N>&</paramtype>
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</parameter>
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<parameter name="y">
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<paramtype>const <classname>array</classname><T, N>&</paramtype>
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</parameter>
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<returns><simpara><code>!(x < y)</code></simpara></returns>
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</function>
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</free-function-group>
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</class>
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</namespace>
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</header>
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</library-reference>
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<section id="array.rationale">
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<title>Design Rationale</title>
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<para>There was an important design tradeoff regarding the
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constructors: We could implement array as an "aggregate" (see
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Section 8.5.1, [dcl.init.aggr], of the C++ Standard). This would
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mean:
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<itemizedlist>
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<listitem><simpara>An array can be initialized with a
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brace-enclosing, comma-separated list of initializers for the
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elements of the container, written in increasing subscript
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order:</simpara>
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<programlisting><classname>boost::array</classname><int,4> a = { { 1, 2, 3 } };</programlisting>
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<simpara>Note that if there are fewer elements in the
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initializer list, then each remaining element gets
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default-initialized (thus, it has a defined value).</simpara>
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</listitem></itemizedlist></para>
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<para>However, this approach has its drawbacks: <emphasis
|
|
role="bold"> passing no initializer list means that the elements
|
|
have an indetermined initial value</emphasis>, because the rule says
|
|
that aggregates may have:
|
|
<itemizedlist>
|
|
<listitem><simpara>No user-declared constructors.</simpara></listitem>
|
|
<listitem><simpara>No private or protected non-static data members.</simpara></listitem>
|
|
<listitem><simpara>No base classes.</simpara></listitem>
|
|
<listitem><simpara>No virtual functions.</simpara></listitem>
|
|
</itemizedlist>
|
|
</para>
|
|
|
|
<para>Nevertheless, The current implementation uses this approach.</para>
|
|
|
|
<para>Note that for standard conforming compilers it is possible to
|
|
use fewer braces (according to 8.5.1 (11) of the Standard). That is,
|
|
you can initialize an array as follows:</para>
|
|
|
|
<programlisting>
|
|
<classname>boost::array</classname><int,4> a = { 1, 2, 3 };
|
|
</programlisting>
|
|
|
|
<para>I'd appreciate any constructive feedback. <emphasis
|
|
role="bold">Please note: I don't have time to read all boost
|
|
mails. Thus, to make sure that feedback arrives to me, please send
|
|
me a copy of each mail regarding this class.</emphasis></para>
|
|
|
|
<para>The code is provided "as is" without expressed or implied
|
|
warranty.</para>
|
|
|
|
</section>
|
|
|
|
<section id="array.more.info">
|
|
<title>For more information...</title>
|
|
<para>To find more details about using ordinary arrays in C++ and
|
|
the framework of the STL, see e.g.
|
|
|
|
<literallayout>The C++ Standard Library - A Tutorial and Reference
|
|
by Nicolai M. Josuttis
|
|
Addison Wesley Longman, 1999
|
|
ISBN 0-201-37926-0</literallayout>
|
|
</para>
|
|
|
|
<para><ulink url="http://www.josuttis.com/">Home Page of Nicolai
|
|
Josuttis</ulink></para>
|
|
</section>
|
|
|
|
<section id="array.ack">
|
|
<title>Acknowledgements</title>
|
|
|
|
<para>Doug Gregor ported the documentation to the BoostBook format.</para>
|
|
</section>
|
|
|
|
<!-- Notes:
|
|
empty() should return N != 0
|
|
size(), empty(), max_size() should be const
|
|
-->
|
|
|
|
</library>
|