Minor tweak: 

  $knob = $_[0] if @_;

[download]
That way, Parent->knob() is an accessor, while Parent->knob(undef) is a mutator that sets the $knob to undef. Slightly better: 
  if (@_)
  {
    # check that $_[0] is allowed.
    $knob = $_[0];
  }

[download]
but that's only if there are invalid values you want to block.

In reply to Re^2: Static Variables in Perl by Tanktalus
in thread Static Variables in Perl by RollyGuy

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