Re: should Octave be more strict about checking number of arguments?

On 7/8/20 9:22 PM, Kai Torben Ohlhus wrote:
> On 7/9/20 1:28 AM, John W. Eaton wrote:
>> Bug report 58695 raised the following issue.
>>
>> Currently, Octave allows function to be called with more input or output
>> arguments than can possibly be used or created.  For example,
>>
>>    function f (), end
>>
>> may be called as
>>
>>    f (1)
>>
>> or
>>
>>    x = f ()   ## You do get a warning here
>>    [1, f, 2]  ## But not here...
>>
>> I think the original intent in Octave was to allow the call warn or
>> attempt to do something reasonable (if possible) when no outputs are
>> created.  So I could see a reasonable argument made for allowing this
>> kind of behavior but I don't know why I thought this was a good thing to
>> do and it seems reasonable to have the interpreter detect these types of
>> argument number mismatches automatically.
>>
>> I think Matlab always throws an error if a function is called with more
>> input or output arguments than can possibly be used or generated so this
>> would improve compatibility somewhat.
>>
>> Should we change Octave's behavior to match Matlab?  Always?  Just when
>> using --traditional mode?
>>
>> jwe
>>
> 
> 
> Previously, I tried to fix bug #58686, where a scenario showed up, that
> should always make Octave follow the Matlab approach in this regard.
> 
> The short outline is, assert() can be called in two ways
> 
>     assert (expr)
>     assert (val, expected)
> 
> Now I made a test like this with your example
> 
>     assert (f(1), 42)
> 
> Because f() returns nothing the call was (without warning or error)
> interpreted as
> 
>     assert (42)  ==  assert (true)
> 
> and passed Octave's test suite en perfect, even my function did not work
> at all.
> 
> Thus with silent argument ignoring it is easily possible to create super
> trivial mistakes, which are a nightmare to detect and to debug as the
> code grows and Octave's test suite is of no help then.
> 
> I vote to always follow the behavior of Matlab in this case or at least
> to throw a warning.

I pushed the following changesets to default:

http://hg.savannah.gnu.org/hgweb/octave/rev/b0b80efecea1
http://hg.savannah.gnu.org/hgweb/octave/rev/5a07c798eb08
http://hg.savannah.gnu.org/hgweb/octave/rev/1dd765e54265

The first makes is an error to call a function with more inputs or 
outputs than the function can accept or produce.  The second fixes 
Octave functions and tests to avoid these errors.  The third change 
fixes tests that expect an error to match the new "function called with 
too many inputs/outputs" error message instead of the older "invalid 
function call" error.

This change is probably too disruptive for stable, but applying it now 
on default should give us time for testing before version 7 is released. 
  If it causes too much trouble, we can generate a warning instead of an 
error by default.

jwe