Ruby Set class: equality of sets
According to the Ruby Set class's documentation, "== Returns true if two sets are equal. The equality of each couple of elements is defined according to Object#eql?.
The essence of this can be demonstrated using Date objects, where sets containing different Date objects but with the same date compare to equal:
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
But using my own objects, where I've coded the eql? method to only compare certain attributes, I can't get it to work.
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}"
The output I get from the above is:
ipdet1 is equal to ipdet11: true
ipdet2 is equal to ipdet12: true
set 1 is equal to set2: false
Any ideas anyone?
When you override eql?
, you also always need to override hash
such that if o1.eql?(o2)
is true, o1.hash == o2.hash
is also true.
For example your hash method could look like this:
def hash
[@ip, @gateway].hash
end
Also you have a typo in your eql?
method: @ip = other.ip
should be @ip == other.ip
.
Also a minor stylenote: if condition then true else false end
is equivalent to just condition
, so your eql?
method can just be defined as
def eql?(other)
@ip == other.ip && @gateway == other.gateway
end
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