A method to override the behavoir of the function slot.
The object of type NodeOutput with the slot to look up.
A character value giving the name of the slot to look up.
Only if name is exactly “value” will the method return the mcarray containing the coda. Otherwise, it returns the result of callNextMethod().
In order to enhance the memory management, coda files are optionally stored on the harddrive in temporary files and loaded on an as needed basis.
By overriding this function, we are able to make this seamless.
Overriding the function slot is a slight abuse and, as such, may in the future be replaced by an accessor function.