ceph/src/boost/doc/test/array2.xml

   1 <section id="array.rationale">
   2    <title>Design Rationale</title>
   3
   4    <para>
   5       There was an important design tradeoff regarding the
   6       constructors: We could implement array as an "aggregate" (see
   7       Section 8.5.1, [dcl.init.aggr], of the C++ Standard). This would
   8       mean:
   9       <itemizedlist>
  10          <listitem>
  11             <simpara>
  12                An array can be initialized with a
  13                brace-enclosing, comma-separated list of initializers for the
  14                elements of the container, written in increasing subscript
  15                order:
  16             </simpara>
  17
  18             <programlisting>
  19                <classname>boost::array</classname>&lt;int,4&gt; a = { { 1, 2, 3 } };
  20             </programlisting>
  21
  22             <simpara>
  23                Note that if there are fewer elements in the
  24                initializer list, then each remaining element gets
  25                default-initialized (thus, it has a defined value).
  26             </simpara>
  27          </listitem>
  28       </itemizedlist>
  29    </para>
  30
  31    <para>
  32       However, this approach has its drawbacks: <emphasis
  33   role="bold">
  34          passing no initializer list means that the elements
  35          have an indetermined initial value
  36       </emphasis>, because the rule says
  37       that aggregates may have:
  38       <itemizedlist>
  39          <listitem>
  40             <simpara>No user-declared constructors.</simpara>
  41          </listitem>
  42          <listitem>
  43             <simpara>No private or protected non-static data members.</simpara>
  44          </listitem>
  45          <listitem>
  46             <simpara>No base classes.</simpara>
  47          </listitem>
  48          <listitem>
  49             <simpara>No virtual functions.</simpara>
  50          </listitem>
  51       </itemizedlist>
  52    </para>
  53
  54    <para>Nevertheless, The current implementation uses this approach.</para>
  55
  56    <para>
  57       Note that for standard conforming compilers it is possible to
  58       use fewer braces (according to 8.5.1 (11) of the Standard). That is,
  59       you can initialize an array as follows:
  60    </para>
  61
  62    <programlisting>
  63       <classname>boost::array</classname>&lt;int,4&gt; a = { 1, 2, 3 };
  64    </programlisting>
  65
  66    <para>
  67       I'd appreciate any constructive feedback. <emphasis
  68   role="bold">
  69          Please note: I don't have time to read all boost
  70          mails. Thus, to make sure that feedback arrives to me, please send
  71          me a copy of each mail regarding this class.
  72       </emphasis>
  73    </para>
  74
  75    <para>
  76       The code is provided "as is" without expressed or implied
  77       warranty.
  78    </para>
  79
  80 </section>
  81
  82