base class.

## Major Features and Improvements

*   `tf.lite`:

    *   New operations supported:
          * tf.unsortedsegmentmin op is supported.
          * tf.atan2 op is supported.
          * tf.sign op is supported.
    *   Updates to existing operations:
          * tfl.mul now supports complex32 inputs.

*   `tf.experimental.StructuredTensor`

A method invocation is similar but the method itself
is specified as a selector upon a value of the receiver type for
the method.
</p>

<pre>
math.Atan2(x, y)  // function call
var pt *Point
pt.Scale(3.5)     // method call with receiver pt
</pre>

<p>
If <code>f</code> denotes a generic function, it must be