attr_reader amend

basket.rb

class Basket
  attr_reader :contents

  def initialize
    @contents = []
  end
end

irb.rb

basket = Basket.new
  #=> #<Basket:0x007f8f92aaf9f0 @contents=[]>

basket.contents
  #=> []

basket.contents = [:flower]
  # NoMethodError: undefined method `contents=' for #<Basket:0x007f8f92aaf9f0>

basket.contents << :flower
  #=> [:flower]

basket.contents
  #=> [:flower]