[Koha-devel] Bug 18539 - Forbid Koha::Objects->find calls in list context

[Jonathan Druart]

Hi Julian,


> @a = Koha::Patrons->find('foo'); # would result in @a = (undef)

And that leads to issues:
if ( @a ) { # = 1
  say $a[0]->borrowernumber; # BOOM
}

See also https://perlmaven.com/how-to-return-undef-from-a-function (was it
the link you were talking about?)

Cheers,
Jonathan

On Wed, 13 Dec 2017 at 10:34 Julian Maurice <julian.maurice at biblibre.com>
wrote:

> Hi developers,
>
> I stumbled upon a line of code recently and I can't figure out why it
> has be done this way. I hope you can help me :)
>
> The line in question is in Koha::Objects::find:
>
>     croak 'Cannot use "->find" in list context' if wantarray;
>
> I read the two bugs (18539 and 18179) and the link given by Jonathan but
> I still don't understand why the call in list context has been
> forbidden. Why not simply return undef (an explicit undef) when no
> records have be found ? It would work as expected in scalar and list
> contexts.
>
> Here is a possible rewrite of 'find' to better explain what I mean:
>
>     sub find {
>         my ( $self, @pars ) = @_;
>
>         my $object = undef;
>
>         @pars = grep { defined } @pars;
>         if (@pars) {
>             my $result = $self->_resultset()->find(@pars);
>             if ($result) {
>                 $object = $self->object_class()->_new_from_dbic($result);
>             }
>         }
>
>         return $object;
>     }
>
> @a = Koha::Patrons->find('foo'); # would result in @a = (undef)
> {a => K::P->find('foo'), b => 'bar'}; # would result in {a => undef, b
> => 'bar'}
>
> Please tell me what you think.
>
> --
> Julian Maurice <julian.maurice at biblibre.com>
> BibLibre
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