In the code example, I pass a hash by value to a sub, push_1, and push one onto the array,

@{ $hash{$key} }

But when I examine the hash after the sub call, the changes are in the hash, but why is this happening. I thought the hash should have the pre function call values.

#!/usr/bin/perl
use strict;
use warnings;
use Data::Dumper;

my %hash;
@hash{ 'a'..'d' } = ([175, 450], [0, 350], [0, 50], [300, 50]);

print "Initial hash\n";
print Dumper \%hash;


print "\nhash after call\n";
push_1(%hash);
print Dumper \%hash;


sub push_1 {
    my %hash = @_;
    for (keys %hash) {
        push @{ $hash{$_} }, 1;
    }
}
__END__
*** Output

C:\perlp>perl t.pl
Initial hash
$VAR1 = {
          'c' => [
                   0,
                   50
                 ],
          'a' => [
                   175,
                   450
                 ],
          'b' => [
                   0,
                   350
                 ],
          'd' => [
                   300,
                   50
                 ]
        };

hash after call
$VAR1 = {
          'c' => [
                   0,
                   50,
                   1
                 ],
          'a' => [
                   175,
                   450,
                   1
                 ],
          'b' => [
                   0,
                   350,
                   1
                 ],
          'd' => [
                   300,
                   50,
                   1
                 ]
        };

C:\perlp>
[download]

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