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[PHP] Re: Should array_udiff be comparing elements from the same array?




On 10 November 2017 at 17:28, Christoph M. Becker <cmbecker69@xxxxxx> wrote:

> On 10.11.2017 at 13:49, Richard Quadling wrote:
>
> > Was testing array_udiff against some complex behaviour. Had an oddity.
> > Reduced the code to a simple test ...
> >
> > 3v4l.org/XON0v
> >
> > <?php
> >
> > $array1 = array(1, 2, 3);
> > $array2 = array(3, 4, 5);
> >
> > print_r(
> >     array_udiff(
> >         $array1,
> >         $array2,
> >         function ($a, $b) {
> >             static $tests = 0;
> >             echo 'array_udiff ', ++$tests, ' ', $a, ' vs ', $b, PHP_EOL;
> >
> >             return ($a < $b) ? -1 : (($a > $b) ? 1 : 0);
> >         }
> >     )
> > );
> >
> >
> > The output is :
> >
> > array_udiff 1 1 vs 2 array_udiff 2 2 vs 3 array_udiff 3 3 vs 4
> array_udiff
> > 4 4 vs 5 array_udiff 5 1 vs 3 array_udiff 6 1 vs 2 array_udiff 7 2 vs 3
> > array_udiff 8 2 vs 3 array_udiff 9 3 vs 3 Array ( [0] => 1 [1] => 2 )
> >
> >
> > Tests 1 and 4 suggests that elements from with a single array are being
> > compared. Is this expected behaviour?
>
> It is not unexpected, if one considers the obvious implementation of the
> function: sort the given arrays first[1], and then do the diff[2].
> Sorting the arrays consequently uses the given comparison function, so
> this can be applied on elements of the same array and on elements of
> different arrays.  Obviously, this requires all arrays to be of the same
> shape, at least with regard to the comparison function.  I think the man
> page should clarify this.
>
> [1]
> <https://github.com/php/php-src/blob/ca1f07b6d733c2f422cb99ffb0e612
> 2b2d5f8b5e/ext/standard/array.c#L5193>
> [2]
> <https://github.com/php/php-src/blob/ca1f07b6d733c2f422cb99ffb0e612
> 2b2d5f8b5e/ext/standard/array.c#L5235>
>
> --
> Christoph M. Becker
>


It would be useful to have the knowledge in the callback that this is the
'sort' phase or the 'filter' phase.

This would also break if the object types were different and the callback
method has typehints for the parameters.

I guess this is one of those sets of methods that did the job perfectly
well, right up to the point someone decided to use it in an different way.

-- 
Richard Quadling