<html> <head> <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> <title>Design Rationale</title> <link rel="stylesheet" href="../boostbook.css" type="text/css"> <meta name="generator" content="DocBook XSL Stylesheets V1.75.2"> <link rel="home" href="../index.html" title="The Boost C++ Libraries BoostBook Documentation Subset"> <link rel="up" href="../array.html" title="Chapter 3. Boost.Array"> <link rel="prev" href="../boost/array.html" title="Class template array"> <link rel="next" href="more/info.html" title="For more information..."> </head> <body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> <table cellpadding="2" width="100%"><tr> <td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../boost.png"></td> <td align="center"><a href="../../../index.html">Home</a></td> <td align="center"><a href="../../../libs/libraries.htm">Libraries</a></td> <td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> <td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> <td align="center"><a href="../../../more/index.htm">More</a></td> </tr></table> <hr> <div class="spirit-nav"> <a accesskey="p" href="../boost/array.html"><img src="../../../doc/html/images/prev.png" alt="Prev"></a><a accesskey="u" href="../array.html"><img src="../../../doc/html/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../doc/html/images/home.png" alt="Home"></a><a accesskey="n" href="more/info.html"><img src="../../../doc/html/images/next.png" alt="Next"></a> </div> <div class="section" title="Design Rationale"> <div class="titlepage"><div><div><h2 class="title" style="clear: both"> <a name="array.rationale"></a>Design Rationale</h2></div></div></div> <p>There was an important design tradeoff regarding the constructors: We could implement array as an "aggregate" (see Section 8.5.1, [dcl.init.aggr], of the C++ Standard). This would mean: </p> <div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"> <p class="simpara">An array can be initialized with a brace-enclosing, comma-separated list of initializers for the elements of the container, written in increasing subscript order:</p> <pre class="programlisting"><code class="computeroutput"><a class="link" href="../boost/array.html" title="Class template array">boost::array</a></code><int,4> a = { { 1, 2, 3 } };</pre> <p class="simpara">Note that if there are fewer elements in the initializer list, then each remaining element gets default-initialized (thus, it has a defined value).</p> </li></ul></div> <p>However, this approach has its drawbacks: <span class="bold"><strong> passing no initializer list means that the elements have an indetermined initial value</strong></span>, because the rule says that aggregates may have: </p> <div class="itemizedlist"><ul class="itemizedlist" type="disc"> <li class="listitem">No user-declared constructors.</li> <li class="listitem">No private or protected non-static data members.</li> <li class="listitem">No base classes.</li> <li class="listitem">No virtual functions.</li> </ul></div> <p> </p> <p>Nevertheless, The current implementation uses this approach.</p> <p>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:</p> <pre class="programlisting"> <code class="computeroutput"><a class="link" href="../boost/array.html" title="Class template array">boost::array</a></code><int,4> a = { 1, 2, 3 }; </pre> <p>I'd appreciate any constructive feedback. <span class="bold"><strong>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.</strong></span></p> <p>The code is provided "as is" without expressed or implied warranty.</p> </div> <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> <td align="left"></td> <td align="right"><div class="copyright-footer">Copyright © 2001-2004 Nicolai M. Josuttis<p>Distributed under the Boost Software License, Version 1.0. (See accompanying file <code class="filename">LICENSE_1_0.txt</code> or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>) </p> </div></td> </tr></table> <hr> <div class="spirit-nav"> <a accesskey="p" href="../boost/array.html"><img src="../../../doc/html/images/prev.png" alt="Prev"></a><a accesskey="u" href="../array.html"><img src="../../../doc/html/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../doc/html/images/home.png" alt="Home"></a><a accesskey="n" href="more/info.html"><img src="../../../doc/html/images/next.png" alt="Next"></a> </div> </body> </html>