kind=defined
names=closed?
visibility=public

--- closed? -> bool
ARGFがcloseされていればtrueを返します。

  # カレントディレクトリから適当にファイルを選ぶ
  ARGV.replace(
    Dir.glob("*").reject{|name| FileTest.file?(name) == false}
  )
  ARGF.each {|line|
    p [ line.chomp, ARGF.filename ]
    ARGF.close
    if ARGF.closed?
      p "ARGF is closed."
    else
      p "ARGF is not closed"
    end
  }
  if ARGF.closed?
    p "ARGF had been closed."
  else
    p "ARGF is not closed"
  end
  
  #例
  #=> ["cat:", "sample.yaml"]
  #=> "ARGF is not closed"
  #=> ["", "test.rb"]
  #=> "ARGF is not closed"
  #=> ["--- !ruby/object:Dog ", "ugo.yaml"]
  #=> "ARGF is closed."
  #=> "ARGF had been closed."

@see [[m:IO#closed?]]

