Ruby doesn't implement x++ for Fixnum's because ???
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From: Tony Arcieri on 4 Nov 2009 13:18 [Note: parts of this message were removed to make it a legal post.] On Wed, Nov 4, 2009 at 10:23 AM, Martin DeMello <martindemello(a)gmail.com>wrote: > And how exactly would you change the value of 1 in place? > Another way to look at it: does Fixnum#+ change the value of its receiver? -- Tony Arcieri Medioh/Nagravision
From: Paul Smith on 4 Nov 2009 13:21 On Wed, Nov 4, 2009 at 6:16 PM, Tony Arcieri <tony(a)medioh.com> wrote: > On Wed, Nov 4, 2009 at 10:23 AM, Martin DeMello <martindemello(a)gmail.com>wrote: > >> And how exactly would you change the value of 1 in place? >> > > You don't. Are you insinuating the behavior of Fixnums isn't already > special cased to begin with? a = 1 a.class #Fixnum a++ # a is now 2 1.class #Fixnum 1++ # Illegal So although a is a Fixnum, and 1 is a Fixnum, they respond to ++ differently? > > -- > Tony Arcieri > Medioh/Nagravision > -- Paul Smith http://www.nomadicfun.co.uk paul(a)pollyandpaul.co.uk
From: RichardOnRails on 4 Nov 2009 14:04 On Nov 4, 9:37 am, Seebs <usenet-nos...(a)seebs.net> wrote: > On 2009-11-04, Marnen Laibow-Koser <mar...(a)marnen.org> wrote: > > > I believe you are quite wrong. If a destructive function like gsub! can > > be implemented as a method, then I see no reason that +=, |=, or postfix > > ++ couldn't be. > > gsub! is implemented as a method on objects which contain data. ++ would > have to be implemented as a method on objects which ARE their data -- which > have no distinction between the object and its "contents". > > gsub! can work because somewhere inside the object there is a hunk of storage > which is separate from the object itself. Fixnum has no such storage to > refer to. > > -s > -- > Copyright 2009, all wrongs reversed. Peter Seebach / usenet-nos...(a)seebs.nethttp://www.seebs.net/log/<-- lawsuits, religion, and funny pictureshttp://en.wikipedia.org/wiki/Fair_Game_(Scientology) <-- get educated! > ++ would have to be implemented as a method on objects which ARE their data Not true. Check out the following, step by step: def show(v) "Got #{v}, class = #{v.class}, object_id = #{v.object_id} (v.object_id-1)/2 = #{(v.object_id-1)/2 }" end class Fixnum def pp # We cant define ++ because of a compiler restriction. self + 1 end end These lines show that a & b values are stored in there object_ids held in the symbol table. Dont believe it? Read more. a = 1; show (a) => Got 1; class = Fixnum; object_id = 3; v >> 1 = 1 b = 1; show (b) => Got 1; class = Fixnum; object_id = 3; v >> 1 = 1 a == b => true Appending these lines shows that a & b values are distinct. That is, after incrementing, a =2, b is unchanged; b is not impacted by as change a += 1; show (a) => Got 2; class = Fixnum; object_id = 5; v >> 1 = 2 show (b) => Got 1; class = Fixnum; object_id = 3; v >> 1 = 1 Appending these lines shows the ++s alias pp works just find a=1; show(a.pp) => Got 2; class = Fixnum; object_id = 5; v >> 1 = 2 show(b) => Got 1; class = Fixnum; object_id = 3; v >> 1 = 1 Appending these lines show that ++ crosses the Fixnum/Bignum boundary a = 2**30-1; show (a) => Got 1073741823; class = Fixnum; object_id = 2147483647; v >> 1 = 1073741823 show(a.pp) => Got 1073741824; class = Bignum; object_id = 22738520; v >> 1 = 11369260 # v >> 1 is irrelevant, of course. Do you agree? Best wishes, Richard
From: Walton Hoops on 4 Nov 2009 14:13 > -----Original Message----- > From: bascule(a)gmail.com [mailto:bascule(a)gmail.com] On Behalf Of Tony > Arcieri > wrote: > I think you're missing why ++ could be useful, and it's precisely > because > Ruby is a "21st century language" > > The ++ operator, far more than just being syntactic sugar for +=1, > would > allow you to send an "increment" message to any object, which would > change > its value in place, i.e. > > def ++ > incrementing_logic_goes_here > end > > I could see this as being handy But you already can with the mechanics of the language that are already present! irb(main):003:0> i=15 => 15 irb(main):004:0> i=i.succ => 16 irb(main):005:0> i="15" => "15" irb(main):006:0> i=i.succ => "16" irb(main):007:0> i=1.2 => 1.2 irb(main):008:0> i=i.succ NoMethodError: undefined method `succ' for 1.2:Float from (irb):8 from /usr/local/bin/irb:12:in `<main>' In an object that it makes sense to increment, define the #succ method! It's that easy!
From: Seebs on 4 Nov 2009 14:13
On 2009-11-04, RichardOnRails <RichardDummyMailbox58407(a)USComputerGurus.com> wrote: > class Fixnum > def pp # We can?t define ++ because of a compiler restriction. > self + 1 > end > end This doesn't seem to do the right thing. a = 1 a.pp Is a now 2? If not, you haven't implemented an increment operator. > Appending these lines shows that a & b values are distinct. > That is, after incrementing, a =2, b is unchanged; b is not > impacted by a?s change > a += 1; show (a) => Got 2; class = Fixnum; object_id = 5; v >> 1 >= 2 > show (b) => Got 1; class = Fixnum; object_id = 3; v >> 1 = 1 Right. You've changed which object a refers to, because you've reassigned a. > Appending these lines shows the ++?s alias pp works just find > a=1; show(a.pp) => Got 2; class = Fixnum; object_id = 5; v >> 1 >= 2 > show(b) => Got 1; class = Fixnum; object_id = 3; v >> 1 = 1 Not the same. The key is that, after "a += 1", not only do you get 2, but a is now 2. > Do you agree? No. For "a.pp" to be the same as a++ in other languages, you'd have to do: a = 1; a.pp; show(a) => Got 2 If you don't get a "2" by using a.pp, it's not an increment, just a "one more than". Consider a loop: a = 1 while ((a += 1) < 10) do puts a end Now, try: a = 1 while (a.pp < 10) do puts a end Doesn't do the same thing. -s -- Copyright 2009, all wrongs reversed. Peter Seebach / usenet-nospam(a)seebs.net http://www.seebs.net/log/ <-- lawsuits, religion, and funny pictures http://en.wikipedia.org/wiki/Fair_Game_(Scientology) <-- get educated! |