# File lib/facet/hash/keys_to_s.rb, line 32
  def keys_to_s!( from_class=nil )
    raise ArgumentError, "Parameter must be a class" unless from_class.kind_of?(Class) if from_class
    if from_class
      self.each_key{ |k| self[k.to_s]=self.delete(k) if k.respond_to?(:to_s) and k.class == from_class }
    else
      self.each_key{ |k| self[k.to_s]=self.delete(k) if k.respond_to?(:to_s) }
    end
    self
  end