class Float
  alias :old_divide :/ 
  def / (other)
    other == 0 ? nil : old_divide(other)
  end
end

##</code><code>##

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

##</code><code>##

use warnings;

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