[Octave-bug-tracker] [bug #50359] clearer documentation for difference between isnull and isempty

[Kai Torben Ohlhus]

Follow-up Comment #24, bug #50359 (project octave):

@Mike: Thank you for the example.  So containers.Map gets refactored regarding
this?  Currently isnull is not used there, so I was not able to find this
example for making it plausible myself.

The documentation is good, only the example can be misleading without knowing
this bug report.


     Return true if X is a special null matrix, string, or single quoted
     string.

     Indexed assignment with such a value on the right-hand side should
     delete array elements.  This function should be used when
     overloading indexed assignment for user-defined classes instead of
     `isempty', to distinguish the cases:

    `A(I) = []'
          This should delete elements if `I' is nonempty.

    `X = []; A(I) = X'
          This should give an error if `I' is nonempty.

     See also: isempty, isindex.


I suggest as example:


    [... as before ...]

    `A(I) = []'

    and

    `X = []; A(I) = X'.

    Assuming in both cases, that `I' is nonempty, the first 
    assignment should delete the respective elements,
    whereas the latter one assigns them an empty matrix, e.g.
    `X' is equivalent to `zeros (0, 0)' in this case and
    will probably result in an error.

     See also: isempty, isindex.


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