delete_if()
  public
  
    
    
Calls the given block once for each
key, value pair in the database. Deletes all entries for
which the block returns true.
Returns self.
   
  
    Show source    
    
      
    def delete_if 
        del_keys = keys.dup
        del_keys.delete_if { |k| yield( k, fetch( k ) ) == false }
        del_keys.each { |k| delete( k ) }
        self
    end