sub increment {
    $_++ foreach @_;
}

my %hash = qw(a 1 b 2 c 3);

increment(%hash);

print "$_ => $hash{$_}\n" for sort keys %hash;

##</code><code>##

a => 2
b => 3
c => 4

##</code><code>##

increment(qw(a 1 b 2 c 3));
...
Modification of a read-only value attempted at...