comparing objects
in [Ruby]
|
From: Robert Klemme on 10 Jun 2010 12:09 On 06/10/2010 05:27 PM, Rein Henrichs wrote: > On 2010-06-10 06:59:40 -0700, Robert Dober said: > >> On Thu, Jun 10, 2010 at 3:41 PM, Wilson Bilkovich <wilsonb(a)gmail.com> >> wrote: >> Even if >>> your code lives in isolation, ensuring proper semantics via these >>> methods prevents a class of tricky bug that your successors may have >>> to deal with. >> Hmm? Would you care to show an example where overloading those methods >> (#eql? and #hash) is needed to ensure proper behavior? I am willing to >> learn. But I am not willing to accept this statement as such. >> Cheers >> R. > > You have been presented with one in this very thread. The OP wants > objects of his class to have the correct semantics for Array#& and > Hash#[], etc. The correct answer is to implement #hash and #eql?, just > as implementing <=> provides objects of his class with the correct > semantics for Array#sort. See also http://blog.rubybestpractices.com/posts/rklemme/018-Complete_Class.html http://blog.rubybestpractices.com/posts/rklemme/019-Complete_Numeric_Class.html Cheers robert -- remember.guy do |as, often| as.you_can - without end http://blog.rubybestpractices.com/
From: Robert Dober on 10 Jun 2010 12:19 On Thu, Jun 10, 2010 at 5:30 PM, Rein Henrichs <reinh(a)reinh.com> wrote: > On 2010-06-10 06:59:40 -0700, Robert Dober said: > You have been presented with one in this very thread. The OP wants objects > of his class to have the correct semantics for Array#& and Hash#[], etc. The > correct answer is to implement #hash and #eql?, just as implementing <=> > provides objects of his class with the correct semantics for Array#sort. I guess you really do not know what I was talking about? Or do you just repeat the same stuff over and over again in order to convince me? overwriting #hash and #eql? breaks Hash! Why the hack should OP's usecase justify this? And it does not answer my question. Where would I like that Hash behaves accordingly to the redefined #eql? and #hash. And BTW I asked Wilson, did I not? Cheers Robert -- The best way to predict the future is to invent it. -- Alan Kay
From: Robert Dober on 10 Jun 2010 12:27 On Thu, Jun 10, 2010 at 6:10 PM, Robert Klemme <shortcutter(a)googlemail.com> wrote: > http://blog.rubybestpractices.com/posts/rklemme/018-Complete_Class.html > http://blog.rubybestpractices.com/posts/rklemme/019-Complete_Numeric_Class.html I You define #eql? and #hash for your convenience. So good, so bad. My question simply was: Show my why *not* redefining #hash and #eql? will cause problems, because that was Wilson's statement. I am still waiting :(. Cheers R. -- The best way to predict the future is to invent it. -- Alan Kay
From: Mark Abramov on 10 Jun 2010 12:48 Robert Dober wrote: > On Thu, Jun 10, 2010 at 5:30 PM, Rein Henrichs <reinh(a)reinh.com> wrote: > overwriting #hash and #eql? breaks Hash! That's not true, I think. -- Posted via http://www.ruby-forum.com/.
From: Robert Dober on 11 Jun 2010 01:52
On Thu, Jun 10, 2010 at 6:48 PM, Mark Abramov <markizko(a)gmail.com> wrote: > Robert Dober wrote: >> On Thu, Jun 10, 2010 at 5:30 PM, Rein Henrichs <reinh(a)reinh.com> wrote: >> overwriting #hash and #eql? breaks Hash! > That's not true, I think. Judge for yourself require "forwardable" def count klass ObjectSpace.each_object( klass ).to_a.size end class N extend Forwardable attr_reader :n def_delegators :n, :hash def eql? otha n == otha.n end private def initialize n @n = n end end # class N h = { N.new( 42 ) => true } h[ N.new( 42 ) ] = 42 p h GC.start p count(N) Cheers R. |