And, this is the way to "directly re-open the method definitions". In fact, it's safer to do it this way than it is to redefine it for the whole program. That kind of "action-at-a-distance" is the source of more maintenance nightmares than anything else.

Totally agree. Before Abigail's post I hadn't really thought of it in OO (obj-oriented and op-overloading) terms. To put what you're saying in, uh, ahem, pseudocode, it's the difference between globally redefining a core method

class Float
  alias :old_divide :/ 
  def / (other)
    other == 0 ? nil : old_divide(other)
  end
end
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and subclassing, which is all good

class MyFloat < Float
  def MyFloat.new(from)
    from.to_f()
  end
  def / (other)
    other == 0 ? nil : super(other)
  end
end
MyFloat.new(4) / 0 # nil
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A last concept to leave you with - if someone were to take your code and wrap it in something else, which is the politer way to handle things?

Sure, it's a library. I was wondering if there was something scoped lexically analogous to:

use warnings;

{
    no warnings qw/once/;
    $foo = 5 - $bar;
}
{
    no warnings qw/uninitialized/;
    $foo = 5 - $qux;
}
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Thanks