在红宝石中实现平等的正确方法是什么 [英] What's the right way to implement equality in ruby

问题描述

对于简单的类结构类：

class Tiger
  attr_accessor :name, :num_stripes
end

正确实现平等的正确方法是什么，以确保 == ， === ， eql？等，这样的实例的班级在组合，散列等方面表现良好。

what is the correct way to implement equality correctly, to ensure that ==, ===, eql?, etc work, and so that instances of the class play nicely in sets, hashes, etc.

编辑

另外，当您要根据未在类外部公开的状态进行比较时，实现平等的一种好方法是什么？例如：

Also, what's a nice way to implement equality when you want to compare based on state that's not exposed outside the class? For example:

class Lady
  attr_accessor :name

  def initialize(age)
    @age = age
  end
end

在这里就像我的平等方法考虑@age一样，但这位女士并没有向客户透露自己的年龄。在这种情况下，我是否必须使用instance_variable_get？

here I'd like my equality method to take @age into account, but the Lady doesn't expose her age to clients. Would I have to use instance_variable_get in this situation?

推荐答案

要简化具有多个状态变量的对象的比较运算符，请创建一个该方法以数组形式返回对象的所有状态。然后只需比较两个状态：

To simplify comparison operators for objects with more than one state variable, create a method that returns all of the object's state as an array. Then just compare the two states:

class Thing

  def initialize(a, b, c)
    @a = a
    @b = b
    @c = c
  end

  def ==(o)
    o.class == self.class && o.state == state
  end

  protected

  def state
    [@a, @b, @c]
  end

end

p Thing.new(1, 2, 3) == Thing.new(1, 2, 3)    # => true
p Thing.new(1, 2, 3) == Thing.new(1, 2, 4)    # => false

此外，如果您希望将类的实例用作哈希键，请添加：

Also, if you want instances of your class to be usable as a hash key, then add:

  alias_method :eql?, :==

  def hash
    state.hash
  end

这些需要公开。

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