ruby - 如何做真正的只读属性(accessors => attributs)

Question

考虑这个简单的代码:

class Yeah
  attr_reader :foo
  attr_reader :fool
  attr_reader :feel
  def initialize(foo: "test", fool: {}, feel: [])
    @foo = foo
    @fool = fool
  end
end

test = Yeah::new
pp test
test.fool[:one] = 10
pp test

输出:

#<Yeah:0x000008019a84a0 @foo="test", @fool={}>
#<Yeah:0x000008019a84a0 @foo="test", @fool={:one=>10}>

我的问题是，有一种“简单”、“干净”的方法，可以对真正的只读数组、哈希属性进行读取访问，或者我需要继承数组或哈希，并带有很多难以编写的锁定，(undef，别名)或使用代理、委托(delegate)或其他像这样的模式？

Answer 1

你可以这样想:

class Yeah
  def self.reader_meth
    %i(foo fool feel).each do |m|
      define_method(m){instance_variable_get("@#{m}").dup.freeze}
    end
  end
  def initialize(foo: "test", fool: {}, feel: [])
    @foo = foo
    @fool = fool
    @feel =feel
  end
  reader_meth
end

test = Yeah.new
test # => #<Yeah:0x8975498 @foo="test", @fool={}, @feel=[]>
test.fool[:one] = 10 # can't modify frozen Hash (RuntimeError)
test # => #<Yeah:0x8975498 @foo="test", @fool={}, @feel=[]>