t is first created.</p>

<p>Often, the optimizer can eliminate bounds- and uniqueness-checks
within an array algorithm, but when that fails, invoking the
same algorithm on <code>body</code>&#39;s argument lets you trade safety for
speed.</p>

<p><strong>Warning:</strong> Do not rely on anything about <code>self</code> (the <code>Array</code>
  that is the target of this method) during the execution of
  <code>body</code>: it may not appear to have its correct value.  Instead,
  use only the <code>UnsafeMuta