I personally think that "bare maps...maps that don't use the output of the map" are not a good idea although other Monks would disagree. Modern Perl versions don't have the older memory penalty of a anon array that cannot be deleted, but the style issue persists.

I think your code could have been written as:

foreach my $num (@$arr)
{
  $hr->{$num} =1;
}
[download]

If you don't have =1, it is easier to see this in a foreach loop. And it means the same thing as your map{}.

#!/usr/bin/perl -w
use strict;

use strict;
use warnings;
use diagnostics;
use Data::Dumper;

my $arr = [1,2,3];
my $hr  = undef;

foreach my $num (@$arr)
{
  $hr->{$num} =1;
}

print Dumper $hr;
__END__
prints:
$VAR1 = {
          '1' => 1,
          '3' => 1,
          '2' => 1
        };
[download]

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