A generic function that can be implemented to modify the first argument to the invoke-callback in simple-i-dispatch.
( this simple-i-dispatch) => this
An object of type simple-i-dispatch.
The generic function
is called by the implementation of simple-i-dispatch to obtain the callback object (first argument) to its
. This allows the object to be computed in some way by subclassing simple-i-dispatch and implementing a method on
specialized for the subclass.
The pre-defined primary method specializing on simple-i-dispatch always returns its argument.