def copy(self):
return self.__class__(name=self.name, valueType=self.valueType, defaultValue=self.defaultValue, hashIndex=self.hashIndex)<EOL>
copy - Create a copy of this IRField.

  Each subclass should implement this, as you'll need to pass in the args to constructor.

@return <IRField (or subclass)> - Another IRField that has all the same values as this one.