fn pub mut field[T: Format](
  name: String,
  value: ref T,
) -> mut ObjectFormatter {
  let start = match @fields {
    case 0 if @named -> '('
    case 0 -> '('
    case _ -> ', '
  }

  @formatter.write(start)
  @formatter.write(name)
  @formatter.write(': ')
  @formatter.descend(fn { value.fmt(@formatter) })
  @fields += 1
  self
}

fn pub mut finish {
  match @fields {
    case 0 if @named -> {}
    case 0 -> @formatter.write('()')
    case _ -> @formatter.write(')')
  }
}