ruby - Ruby 的 Hash 在比较键时使用哪种相等性测试？

Question

我有一个围绕一些对象的包装类，我想将这些对象用作散列中的键。包装对象和解包装对象应映射到相同的键。

一个简单的例子是这样的:

class A
  attr_reader :x
  def initialize(inner)
    @inner=inner
  end
  def x; @inner.x; end
  def ==(other)
    @inner.x==other.x
  end
end
a = A.new(o)  #o is just any object that allows o.x
b = A.new(o)
h = {a=>5}
p h[a] #5
p h[b] #nil, should be 5
p h[o] #nil, should be 5

我试过 ==、===、eq?并散列所有无济于事。

Answer 1

Hash uses key.eql? to test keys for equality. If you need to use instances of your own classes as keys in a Hash, it is recommended that you define both the eql? and hash methods. The hash method must have the property that a.eql?(b) implies a.hash == b.hash.

所以...

class A
  attr_reader :x
  def initialize(inner)
    @inner=inner
  end
  def x; @inner.x; end
  def ==(other)
    @inner.x==other.x
  end

  def eql?(other)
    self == other
  end

  def hash
    x.hash
  end
end