comparing objects
in [Ruby]
|
From: Caleb Clausen on 11 Jun 2010 15:11 On 6/11/10, Robert Dober <robert.dober(a)gmail.com> wrote: > OP wanted to use Array#&, and Array#&, for a reason not too clear to > me, uses Object#eql? instead of Object#== I did discourage the > overloading of Object#eql? and Object#hash for *that purpose*. Array#& uses eql? instead of == because internally, it works something like this: class Array def &(other) h1={} other.each{|x| h1[x]=true} select{|x| h1[x] } end end In other words, it creates a (hash) index to get a speedup. (From O(M*N) to O(M+N).)
From: Robert Dober on 11 Jun 2010 15:56 On Fri, Jun 11, 2010 at 9:11 PM, Caleb Clausen <vikkous(a)gmail.com> wrote: I see, thanx :)
From: Robert Klemme on 12 Jun 2010 04:51 On 06/11/2010 08:15 PM, Robert Dober wrote: > On Fri, Jun 11, 2010 at 6:47 PM, Robert Klemme > <shortcutter(a)googlemail.com> wrote: >> On 10.06.2010 18:27, Robert Dober wrote: >>> 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 :(. >> The advice to implement #eql? and #hash really only makes sense if >> equivalence can reasonably be defined for a class and if instances of that >> class should be used as Hash keys or in Set. If not at least equivalence >> can be defined other than via identity (which is the default) then it is >> perfectly reasonable to not override both methods and go with the default >> implementation. > But that was *exactly* my point. I don't think we disagree, nor do I argue with you. I just posted blog links as illustration to Rein's point about how to implement those methods. Kind regards robert -- remember.guy do |as, often| as.you_can - without end http://blog.rubybestpractices.com/
From: Robert Dober on 12 Jun 2010 05:01 On Sat, Jun 12, 2010 at 10:55 AM, Robert Klemme <shortcutter(a)googlemail.com> wrote: > I don't think we disagree, nor do I argue with you. I just posted blog > links as illustration to Rein's point about how to implement those methods. Forgive my confusion then. Cheers Robert -- The best way to predict the future is to invent it. -- Alan Kay
From: Robert Klemme on 12 Jun 2010 11:36
On 12.06.2010 11:01, Robert Dober wrote: > On Sat, Jun 12, 2010 at 10:55 AM, Robert Klemme > <shortcutter(a)googlemail.com> wrote: > >> I don't think we disagree, nor do I argue with you. I just posted blog >> links as illustration to Rein's point about how to implement those methods. > > Forgive my confusion then. No problem. I think I fueled it by not including a comment in the original posting. Sorry for that. Kind regards robert -- remember.guy do |as, often| as.you_can - without end http://blog.rubybestpractices.com/ |