when<TResult extends Object?>  method 
- @optionalTypeArgs
- required TResult resultAvailable(- ResultAvailable data
 
- required TResult unknown(),
A switch-like method, using callbacks.
As opposed to map, this offers destructuring.
It is equivalent to doing:
switch (sealedClass) {
  case Subclass(:final field):
    return ...;
  case Subclass2(:final field2):
    return ...;
}
Implementation
@optionalTypeArgs TResult when<TResult extends Object?>({required TResult Function( ResultAvailable data)  resultAvailable,required TResult Function( ResultUnavailable data)  resultUnavailable,required TResult Function( Map<String, dynamic> data)  unknown,}) {final _that = this;
switch (_that) {
case UTempCheckHandleAvailabilityResultResultAvailable():
return resultAvailable(_that.data);case UTempCheckHandleAvailabilityResultResultUnavailable():
return resultUnavailable(_that.data);case UTempCheckHandleAvailabilityResultUnknown():
return unknown(_that.data);}
}