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require 'stringio'

old_out = $stdout

class TeeIO < StringIO
  def initialize(stdout)
    super()
    @stdout = stdout
  end

  def write(*args)
    super
    @stdout.write(*args)
  end
end

class ProxyIO < BasicObject
  def initialize(*streams)
    @streams = streams
  end

  private

  def method_missing(name, *args, &block)
    result = nil
    @streams.each do |stream|
      result = stream.send(name, *args, &block)
    end
    result
  end
end

$stdout = tee = TeeIO.new(old_out)
puts "hello world!"
$stdout = old_out
puts "From tee:"
puts tee.string

$stdout = ProxyIO.new(old_out, stringio = StringIO.new)
puts "hello again!"
$stdout = old_out
puts "From proxy:"
puts stringio.string