PDF::Writer：PDF::SimpleTable#position, #position=

require 'pdf/simpletable'

pdf = PDF::Writer.new

def table(pdf, position)
  PDF::SimpleTable.new do |tab|
    tab.column_order = %w(col1 col2 col3)

    p tab.position
    tab.position = position

    tab.show_lines = :all

    data = [
      { "col1" => "foo", "col2" => "bar", "col3" => "baz" },
    ]

    tab.data.replace data
    tab.render_on(pdf)
  end
end

[:left, :right, :center, 35, -35].each do |position|
  table(pdf, position)
end

pdf.save_as("2008041200.pdf")

で、

:center
:center
:center
:center
:center