Also beware of circular references. A variable that refers to itself or a set or
variables that create a closed loop of references can be a memory leak.

What not to do:

{
   my ($x,$y);
    $x = \$y;    # These will last until exit
    $y = \$x;
}

{
    my $x;
    $x = \$x;    # This will last also
}
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