def to_hash
        h = {}
        keys.each { |k| h[ k ] = self.fetch( k ) }
        h
    end
def to_hash
        h = {}
        keys.each { |k| h[ k ] = self.fetch( k ) }
        h
    end
:call-seq:
   ydbm.to_hash -> hash

 Converts the contents of the database to an in-memory Hash object, and
 returns it.