Ruby Set类:集合的相等性

Question

根据Ruby Set类的文档,"==如果两个集合相等则返回true.每个元素的相等性是根据Object#eql？定义的.

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,我无法让它工作.

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

任何人的想法？

Answer 1

当你覆盖时eql?,你也总是需要覆盖hashif if o1.eql?(o2)为true,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

你的eql?方法也有一个错字:@ip = other.ip应该是@ip == other.ip.

另外一个小样式:if condition then true else false end相当于just condition,所以你的eql?方法可以定义为

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