Re: Expected behavior for variables which shadow function names

[Daniel J Sebald]

On 03/07/2013 12:18 PM, Rik wrote:
> 3/7/13
>
> All,
>
> I ran across an odd behavior and I wanted to know what other people thought
> was "correct".
>
> For the following function:
>
> function y = tstflag (flag)
>    y = flag;
> endfunction
>
> When called with any argument it behaves as expected.
>
> x = tstflag (1)
> x =  1
> x = tstflag ([])
> x = [](0x0)
>
> When called with no arguments, however, the return value is expanded to the
> output of the flag() function which is a 64x3 matrix.
>
> x = tstflag ()
> x =
>
>     1   0   0
>     1   1   1
>     0   0   1
>     0   0   0
>     ...
>
> I understand what is happening, either the flag() function is shadowed by
> the local variable or it isn't, but I wonder what Matlab does for this
> corner case?  I naively assumed that no input would be similar to a null
> input ([]).  I can always get around this by assigning a default value to
> flag in the function header.

I would make the same assumption.  This is potentially problematic and, 
at minimum, confusing to someone not paying real close attention.  I 
suppose this is all avoided if one programs the script file to check the 
number of input arguments.  However, as you've shown it can lead to 
unexpected results for valid routines not much more complex than the 
example you gave.

It seems to me the proper behavior for tstflag() would be to issue an 
error message similar to the following where I've change the variable 
reference to "flig" instead of "flag":

octave:10> x = tstflag()
error: `flig' undefined near line 3 column 7
error: called from:
error:   /home/sebaldd/octave/tstflag.m at line 3, column 5

Dan