boost_1_45_0/doc/test/array2.xml

<section id="array.rationale">
   <title>Design Rationale</title>

   <para>
      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:
      <itemizedlist>
         <listitem>
            <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:
            </simpara>

            <programlisting>
               <classname>boost::array</classname>&lt;int,4&gt; a = { { 1, 2, 3 } };
            </programlisting>

            <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).
            </simpara>
         </listitem>
      </itemizedlist>
   </para>

   <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>&lt;int,4&gt; 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>