class Tins::LinesFile

def initialize(lines, line_number = nil)
  @lines = lines
  @lines.each_with_index do |line, i|
    line.extend LineExtension
    line.instance_variable_set :@line_number, i + 1
    line.instance_variable_set :@lines_file, self
  end
  instance_variable_set :@line_number, line_number || (@lines.empty? ? 0 : 1)
end