Ruby 设置类 : equality of sets

Question

根据 Ruby Set 类的文档，“== 如果两个集合相等，则返回 true。每对元素的相等性根据 Object#eql? 定义。

可以使用 Date 对象来演示其本质，其中包含不同 Date 对象但具有相同日期的集合比较相等:

require 'set'
d1 = Date.today              # => Thu, 30 Sep 2010
puts d1.object_id            # => 2211539680
d2 = Date.today + 1          # => Fri, 01 Oct 2010
puts d2.object_id            # => 2211522320
set1 = Set.new([d1, d2])

d11 = Date.today             # => Thu, 30 Sep 2010
puts d11.object_id           # => 2211489080
d12 = Date.today + 1         # => Fri, 01 Oct 2010
puts d12.object_id           # => 2211469380
set2 = Set.new([d12, d11])

set1 == set2                 # => true

但是使用我自己的对象，我在哪里编写了 eql？方法只比较某些属性，我不能让它工作。

class IpDet

    attr_reader :ip, :gateway

    def initialize(ip, gateway, netmask, reverse)
        @ip = ip
        @gateway = gateway
        @netmask = netmask
        @reverse = reverse
    end

    def eql?(other)
        if @ip = other.ip && @gateway == other.gateway
            return true
        else
            return false
        end
    end
end



ipdet1 = IpDet.new(123456, 123457, 123458, 'example.com')
ipdet2 = IpDet.new(234567, 2345699, 123458, 'nil')

ipdet11 = IpDet.new(123456, 123457, 777777, 'other_domain.com')
ipdet12 = IpDet.new(234567, 2345699, 777777, 'example.com')

puts "ipdet1 is equal to ipdet11: #{ipdet1.eql?(ipdet11)}"
puts "ipdet2 is equal to ipdet12: #{ipdet2.eql?(ipdet12)}"


set1 = Set.new([ipdet1, ipdet2])
set2 = Set.new([ipdet11, ipdet12])

puts "set 1 is equal to set2: #{set1 == set2}"

我从上面得到的输出是:

ipdet1 is equal to ipdet11: true
ipdet2 is equal to ipdet12: true
set 1 is equal to set2: false

有什么想法吗？

Answer 1

当你覆盖 eql? 时，你也总是需要覆盖 hash 使得如果 o1.eql?(o2) 为真， o1.hash == o2.hash 也是如此。

例如，您的哈希方法可能如下所示:

def hash
  [@ip, @gateway].hash
end

您的 eql? 方法中还有一个错字:@ip = other.ip 应该是 @ip == other.ip .

还有一个小风格注释:if condition then true else false end 仅相当于 condition，所以你的 eql? 方法可以是定义为

def eql?(other)
  @ip == other.ip && @gateway == other.gateway
end