<section id="array.intro"> | |
<title>Introduction</title> | |
<using-namespace name="boost"/> | |
<using-class name="array"/> | |
<para>The C++ Standard Template Library STL as part of the C++ | |
Standard Library provides a framework for processing algorithms on | |
different kind of containers. However, ordinary arrays don't | |
provide the interface of STL containers (although, they provide | |
the iterator interface of STL containers).</para> | |
<para>As replacement for ordinary arrays, the STL provides class | |
<code><classname>std::vector</classname></code>. However, | |
<code><classname>std::vector<></classname></code> provides | |
the semantics of dynamic arrays. Thus, it manages data to be able | |
to change the number of elements. This results in some overhead in | |
case only arrays with static size are needed.</para> | |
<para>In his book, <emphasis>Generic Programming and the | |
STL</emphasis>, Matthew H. Austern introduces a useful wrapper | |
class for ordinary arrays with static size, called | |
<code>block</code>. It is safer and has no worse performance than | |
ordinary arrays. In <emphasis>The C++ Programming | |
Language</emphasis>, 3rd edition, Bjarne Stroustrup introduces a | |
similar class, called <code>c_array</code>, which I (<ulink | |
url="http://www.josuttis.com">Nicolai Josuttis</ulink>) present | |
slightly modified in my book <emphasis>The C++ Standard Library - | |
A Tutorial and Reference</emphasis>, called | |
<code>carray</code>. This is the essence of these approaches | |
spiced with many feedback from <ulink | |
url="http://www.boost.org">boost</ulink>.</para> | |
<para>After considering different names, we decided to name this | |
class simply <code><classname>array</classname></code>.</para> | |
<para>Note that this class is suggested to be part of the next | |
Technical Report, which will extend the C++ Standard (see | |
<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> | |
<para>Class <code><classname>array</classname></code> fulfills most | |
but not all of the requirements of "reversible containers" (see | |
Section 23.1, [lib.container.requirements] of the C++ | |
Standard). The reasons array is not an reversible STL container is | |
because: | |
<itemizedlist spacing="compact"> | |
<listitem><simpara>No constructors are provided.</simpara></listitem> | |
<listitem><simpara>Elements may have an undetermined initial value (see <xref linkend="array.rationale"/>).</simpara></listitem> | |
<listitem><simpara><functionname>swap</functionname>() has no constant complexity.</simpara></listitem> | |
<listitem><simpara><methodname>size</methodname>() is always constant, based on the second template argument of the type.</simpara></listitem> | |
<listitem><simpara>The container provides no allocator support.</simpara></listitem> | |
</itemizedlist> | |
</para> | |
<para>It doesn't fulfill the requirements of a "sequence" (see Section 23.1.1, [lib.sequence.reqmts] of the C++ Standard), except that: | |
<itemizedlist spacing="compact"> | |
<listitem><simpara><methodname>front</methodname>() and <methodname>back</methodname>() are provided.</simpara></listitem> | |
<listitem><simpara><methodname>operator[]</methodname> and <methodname>at</methodname>() are provided.</simpara></listitem> | |
</itemizedlist> | |
</para> | |
</section> | |