Cocoa/Swift 3.0 replacement for NSNumberFormatter.isPartialStringValid
<p>In a Swift Cocoa app for macOS I inherited from NSNumberFormatter and have overridden isPartialStringValid. After migrating to Swift 3.0 I now have to subclass NumberFormatter and I get the error "Method does not override any method from its superclass". With what could I replace the method?</p>

<pre><code>override func isPartialStringValid(_ partialString: String, newEditingString newString: AutoreleasingUnsafeMutablePointer&lt;AutoreleasingUnsafeMutablePointer&lt;NSString?&gt;&gt;?, errorDescription error: AutoreleasingUnsafeMutablePointer&lt;AutoreleasingUnsafeMutablePointer&lt;NSString?&gt;&gt;?) -&gt; Bool { ... }
</code></pre>