an test whether a value is available.</td>
</tr>
<tr>
<td class="IconColumn">
<img src="../../GFX/PublicInterface.gif" alt="Public Interface" /></td>
<td><a href="../../Contents/1/251.html">IValue&lt;T&gt;</a></td>
<td>A read-only encapsulated value.</td>
</tr>
<tr>
<td class="IconColumn">
<img src="../../GFX/PublicInterface.gif" alt="Public Interface" /></td>
<td><a href="../../Contents/1/252.html">IVolatile&lt;T&gt;</a></td>
<td>A volatile value.</td>
</tr>
</table>
<div class="TopLink"><a 