# File lib/mongo/util/write_concern.rb, line 25
    def write_concern_from_legacy(opts)
      # Warn if 'safe' parameter is being used,
      if opts.key?(:safe) && !@@safe_warn && !ENV['TEST_MODE']
        warn "[DEPRECATED] The 'safe' write concern option has been deprecated in favor of 'w'."
        @@safe_warn = true
      end

      # nil:   set :w => 0
      # false: set :w => 0
      # true:  set :w => 1
      # hash:  set :w => 0 and merge with opts

      unless opts.has_key?(:w)
        opts[:w] = 0 # legacy default, unacknowledged
        safe     = opts.delete(:safe)
        if(safe && safe.is_a?(Hash))
          opts.merge!(safe)
        elsif(safe == true)
          opts[:w] = 1
        end
      end
    end