Hi monks,

I'm trying to understand the behavior of the given-when construct
when I use an array reference in the "when" clause.
I saw a similar example in "Programming Perl - 4th ed."
but it's not doing what I expected.
I have this test case: 

#!/usr/bin/env perl

use v5.14;

my @array = (0, 1000..10_000, 'abcd');

for my $element (qw/a ab abc 100 1000 10000 abcd/) {
   say "With grep:";
   if (grep {/^$element$/} @array) {
      say "Element $element is there";
   } else {
      say "Element $element is not there";
   }
   
   say "With given-when:";
   given ($element) {
      when (\@array) {
         say "Element $element is there";
      }
      default {
         say "Element $element is not there";
      }
   }
   say "";
}

[download]


It yields this result: 

With grep:
Element a is not there
With given-when:
Element a is there

With grep:
Element ab is not there
With given-when:
Element ab is there

With grep:
Element abc is not there
With given-when:
Element abc is there

With grep:
Element 100 is not there
With given-when:
Element 100 is not there

With grep:
Element 1000 is there
With given-when:
Element 1000 is there

With grep:
Element 10000 is there
With given-when:
Element 10000 is there

With grep:
Element abcd is there
With given-when:
Element abcd is there

[download]


The 'grep' gets it right every time.
The given-when construct finds elements 'a', 'ab' and 'abc' even if the're not in @array.

The funny thing is: if I remove the 0 from @array,
elements 'a', 'ab' and 'abc' are reported as "not there",
so the matching element seems to be the 0.
I'm rather puzzled.

Can someone explain this?

Thanks, bye.

In reply to given-when construct unexpected behavior with arrays by mantager

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