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| 26 | <div class="titlepage"><div><div><h3 class="title"> |
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| 27 | <a name="array.rationale"></a>Design Rationale</h3></div></div></div> |
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| 28 | <p>There was an important design tradeoff regarding the |
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| 29 | constructors: We could implement array as an "aggregate" (see |
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| 30 | Section 8.5.1, [dcl.init.aggr], of the C++ Standard). This would |
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| 31 | mean: |
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| 32 | </p> |
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| 33 | <div class="itemizedlist"><ul type="disc"><li> |
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| 34 | <p>An array can be initialized with a |
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| 35 | brace-enclosing, comma-separated list of initializers for the |
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| 36 | elements of the container, written in increasing subscript |
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| 37 | order:</p> |
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| 38 | <pre class="programlisting"><code class="computeroutput"><a href="../boost/array.html" title="Class template array">boost::array</a></code><int,4> a = { { 1, 2, 3 } };</pre> |
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| 39 | <p>Note that if there are fewer elements in the |
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| 40 | initializer list, then each remaining element gets |
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| 41 | default-initialized (thus, it has a defined value).</p> |
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| 42 | </li></ul></div> |
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| 43 | <p>However, this approach has its drawbacks: <span class="bold"><strong> passing no initializer list means that the elements |
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| 44 | have an indetermined initial value</strong></span>, because the rule says |
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| 45 | that aggregates may have: |
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| 46 | </p> |
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| 47 | <div class="itemizedlist"><ul type="disc"> |
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| 48 | <li>No user-declared constructors.</li> |
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| 49 | <li>No private or protected non-static data members.</li> |
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| 50 | <li>No base classes.</li> |
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| 51 | <li>No virtual functions.</li> |
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| 52 | </ul></div> |
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| 53 | <p>Nevertheless, The current implementation uses this approach.</p> |
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| 54 | <p>Note that for standard conforming compilers it is possible to |
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| 55 | use fewer braces (according to 8.5.1 (11) of the Standard). That is, |
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| 56 | you can initialize an array as follows:</p> |
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| 57 | <pre class="programlisting"><code class="computeroutput"><a href="../boost/array.html" title="Class template array">boost::array</a></code><int,4> a = { 1, 2, 3 }; |
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| 58 | </pre> |
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| 59 | <p>I'd appreciate any constructive feedback. <span class="bold"><strong>Please note: I don't have time to read all boost |
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| 60 | mails. Thus, to make sure that feedback arrives to me, please send |
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| 61 | me a copy of each mail regarding this class.</strong></span></p> |
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| 62 | <p>The code is provided "as is" without expressed or implied |
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| 63 | warranty.</p> |
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| 64 | </div> |
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| 66 | <td align="left"></td> |
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| 67 | <td align="right"><small>Copyright © 2001-2004 Nicolai M. Josuttis</small></td> |
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