p>Returns true if a value is present in the implementation passed in. Constexpr, never throws.</p><li>
	<a href="../reference/policies/base/has_error.html" ><code>static bool _has_error(Impl &amp;&amp;) noexcept</code></a>
<p>Returns true if an error is present in the implementation passed in. Constexpr, never throws.</p><li>
	<a href="../reference/policies/base/has_exception.html" ><code>static bool _has_exception(Impl &amp;&amp;) noexcept</code></a>
<p>Returns true if an exception is present in the implem