attr_reader_test.rb

class Person
  def initialize
    @attributes = {}
  end

  def attributes
    @attributes.dup.freeze
  end

  def name
    @attributes[:name]
  end
end

john_doe = Person.new
# #<Person:0x007fa713c56d60 @attributes={}>

john_doe.attributes
# {}

john_doe.attributes[:name] = "John Doe"
# RuntimeError: can't modify frozen Hash

john_doe.name
# nil