class Hoge def initialize @data = [*1..10] end attr_reader :data end h = Hoge.new hoge.data = 1 #=>Error p hoge.data #=>[1, 2, 3, 4, 5, 6, 7, 8, 9, 10] hoge.data[0] = 0 p hoge.data #=>[0, 2, 3, 4, 5, 6, 7, 8, 9, 10] hoge.data = 1 がエラー…