Hello Monks!-

I think I need a knowledge recharge on the 'or' versus '||' question, as I'm finding the attached program's results hard to explain.

To start at the beginning, I have a Tk canvas that may or may not have someting on it. I used this syntax... 

my @coords = $can->bbox('all') || ( 0, 0, 5, 5);

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...to try and have @coords = (0, 0, 5, 5) if the canvas was empty, otherwise have the coordinates of the surrounding box for all its contents.

This didn't work the way I wanted it to, so I came up with this program, partially for fun, and partially to help me understand things better: 

use strict;
use warnings;
use Data::Dumper;
use Tk;

sub x { return () };

my @list = x() | (1,2,3);
print "List:\n",Dumper(\@list), "\n";
my @list0 = x() || (1,2,3);
print "List0:\n",Dumper(\@list0), "\n";
my @list1 = x() or (1,2,3);
print "List1:\n",Dumper(\@list1), "\n";

my $t=MainWindow->new();
my $c=$t->Scrolled('Canvas')->pack;
$c->createArc(5,5,100,100);
$t->update;
my @list2 = $c->bbox('all') || (1,2,3);
print "List2:\n", Dumper(\@list2), "\n";

my @list3 = $c->bbox('all') or (1,2,3);
print "List3:\n", Dumper(\@list3), "\n";

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My output looks like this: 
Useless use of a constant in void context at /tmp/crap line 10.
Useless use of a constant in void context at /tmp/crap line 14.
Useless use of a constant in void context at /tmp/crap line 14.
Useless use of a constant in void context at /tmp/crap line 24.
Useless use of a constant in void context at /tmp/crap line 24.
Use of uninitialized value in bitwise or (|) at /tmp/crap line 10.
List:
$VAR1 = [
          3
        ];

List0:
$VAR1 = [
          1,
          2,
          3
        ];

List1:
$VAR1 = [];

List2:
$VAR1 = [
          [
            51,
            3,
            102,
            55
          ]
        ];

List3:
$VAR1 = [
          51,
          3,
          102,
          55
        ];

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I see that the warnings are trying to tell me something, but it's not clear enough to me what that problem(s) is (are).

LIST: was just for fun, but I don't understand why I got what I got

LIST0: I think I understand this one, but then...
LIST1: ...why doesn't this work as well?

LIST2: I really don't understand how I get a list of a list here, and then...
LIST3: ...I'm not sure I understand why this works!

Many thanks in advance for your guidance.

-Craig

In reply to 'or' versus '||' - Unexpected Results by cmv

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