class Hash

  # Returns true if the hash contains
  # _only_ the given keys, otherwise false.
  #
  #   h = { :a => 1, :b => 2 }
  #   h.has_only_keys?( :a, :b )   #=> true
  #   h.has_only_keys?( :a )       #=> false
  #
  def has_only_keys?(*check_keys)
    unknown_keys = self.keys - check_keys
    return unknown_keys.empty?
  end

end


#  _____         _
# |_   _|__  ___| |_
#   | |/ _ \/ __| __|
#   | |  __/\__ \ |_
#   |_|\___||___/\__|
#
=begin test

  require 'test/unit'

  class TCHash < Test::Unit::TestCase

    def test_has_only_keys?
      assert( { :a=>1,:b=>2,:c=>3 }.has_only_keys?(:a,:b,:c) )
      assert( ! { :a=>1,:b=>2,:c=>3 }.has_only_keys?(:a,:b) )
    end

  end

=end