vided by this stream.</p>
<p>Compares each element of this stream to <code>needle</code> using <a href="dart-core/Object/operator_equals.html">Object.==</a>.
If an equal element is found, the returned future is completed with <code>true</code>.
If this stream ends without finding a match, the future is completed with
<code>false</code>.</p>
<p>If this stream emits an error, or the call to <a href="dart-core/Object/operator_equals.html">Object.==</a> throws,
the returned future is completed with that error,
