# Please explain nuances of ||= **URL:** \ **Category:** Ruby\ **Created:** [May 1, 2008, 6:20pm UTC](https://www.ruby-forum.com/t/please-explain-nuances-of/136398 "2008-05-01T18:20:27Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![rubyfreak](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e9c0ed/32.png) [@rubyfreak](https://www.ruby-forum.com/u/rubyfreak)\ **Post date:** [May 1, 2008, 6:20pm UTC](https://www.ruby-forum.com/t/please-explain-nuances-of/136398/1 "2008-05-01T18:20:27Z")
I am reading some of the ruby files in rails and I an seeing the ||= method used a lot. knowing ruby the way I do, I realize that she has lots of magical surprises and I really want to get to know this girl! Consider the initialize method of resources.rb 51 def initialize(entities, options) 52 @plural ||= entities 53 @singular ||= options[:singular] || plural.to\_s.singularize 54 @path\_segment = options.delete(:as) || @plural 55 56 @options = options 57 58 arrange\_actions 59 add\_default\_actions 60 set\_prefixes 61 end (OK, so one iddy bitty part of this is a rails question, and dangit, this is a ruby forum, but you guys are smarter and have better haircuts) Question (1) After several hours of searching I find virtually nothing that fully explains the line @singular ||= options[:singular] || plural.to\_s.singularize I think know what is does, It assigns @singular a value for a “singular named” controller if the options hash contains the symbol :singular. I am looking more for a full description of how ||= and it’s friends like &&= actually work. my current understanding shows me: @singular = (options[:singular]) or (plural.to\_s.singularize) but the full logic seems to be more like: if options contains a symbol named :singular then @singular = plural.to\_s.singularize end if But what is the value of @singular if there is no :singular symbol? nil? What I think is going on is a lot more like an IF statement than a OR statement. Question (2) in the line: @plural ||= entities if entities is (false?, nil? something that fails “OR”) what happens to @plural? Once again, the ||= seems more like an “equals If” statement rather than an “equals Or” statement. Question (3) @path\_segment = options.delete(:as) || @plural So @path\_segment is assigned either the return from the delete operation (:as) ? or the plural name of the controller. Is that correct? Where in a common resourceful routes mapping is there an :as? Thanks in advance for any help. ---
**Author:** ![rubyfreak](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e9c0ed/32.png) [@rubyfreak](https://www.ruby-forum.com/u/rubyfreak)\ **Post date:** [May 1, 2008, 6:34pm UTC](https://www.ruby-forum.com/t/please-explain-nuances-of/136398/2 "2008-05-01T18:34:39Z")
You’re close on some, right on some. @plural||=entries simply says, if @plural is nil or false (someone correct me if I’m a tad off), set it to entries, otherwise don’t do anything. For @singular, close but… you need the or @singular ||= ((options[:singular]) or (plural.to\_s.singularize)) @path\_segment is a little bit stranger, but for me it harkens back to c days. if options.delete(:as) returns any value that evalutes to true (anything but nil or false), @path\_segment is set to that value. If options.delete(:as) fails or returns nil, @path\_segment is set to @plural. Does that help? ---
**Author:** ![rubyfreak](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e9c0ed/32.png) [@rubyfreak](https://www.ruby-forum.com/u/rubyfreak)\ **Post date:** [May 1, 2008, 6:37pm UTC](https://www.ruby-forum.com/t/please-explain-nuances-of/136398/3 "2008-05-01T18:37:36Z")
On 2008-05-01, Ruby F. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > I am reading some of the ruby files in rails and I an seeing the ||= > method used a lot. There’s a nice discussion at URL:http://talklikeaduck.denhaven2.com/articles/2008/04/26/x-y-redux. Regards, Jeremy H. ---
**Author:** ![rubyfreak](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e9c0ed/32.png) [@rubyfreak](https://www.ruby-forum.com/u/rubyfreak)\ **Post date:** [May 1, 2008, 6:57pm UTC](https://www.ruby-forum.com/t/please-explain-nuances-of/136398/4 "2008-05-01T18:57:06Z")
Hi – On Fri, 2 May 2008, Ruby F. wrote: > I am reading some of the ruby files in rails and I an seeing the ||= > method used a lot. > knowing ruby the way I do, I realize that she has lots of magical > surprises and I really want to get to know this girl! x ||= y means: x || x = y The difference is that x ||= y won’t complain if x is undefined, whereas if you type x || x = y and there’s no x in scope, it will. The basic idea is that if x is (a) undefined (b) nil (c) false, you want to set it to y. Otherwise, you want to leave it alone. The whole expression evaluates to x, after the assignment has happened (or not). See [http://dablog.rubypal.com/2008/3/25/a-short-circuit-edge-case](http://dablog.rubypal.com/2008/3/25/a-short-circuit-edge-case) for more. David ---
**Author:** ![rubyfreak](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e9c0ed/32.png) [@rubyfreak](https://www.ruby-forum.com/u/rubyfreak)\ **Post date:** [May 1, 2008, 9:06pm UTC](https://www.ruby-forum.com/t/please-explain-nuances-of/136398/5 "2008-05-01T21:06:57Z")
- David A. Black [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) (18:56) schrieb: > Hi – > > On Fri, 2 May 2008, Ruby F. wrote: > > > I am reading some of the ruby files in rails and I an seeing the ||= > > method used a lot. > > knowing ruby the way I do, I realize that she has lots of magical > > surprises and I really want to get to know this girl! > > x ||= y means: x || x = y No, it means: x = x || y > The difference is that x ||= y won’t complain if x is undefined, That’s because = does the same. mfg, simon … l ---
**Author:** ![rubyfreak](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e9c0ed/32.png) [@rubyfreak](https://www.ruby-forum.com/u/rubyfreak)\ **Post date:** [May 1, 2008, 7:10pm UTC](https://www.ruby-forum.com/t/please-explain-nuances-of/136398/6 "2008-05-01T19:10:38Z")
Yes, Thank you, That is very helpful. Google seems to puke on “||=” so I wasn’t getting any search results. ---
**Author:** ![rubyfreak](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e9c0ed/32.png) [@rubyfreak](https://www.ruby-forum.com/u/rubyfreak)\ **Post date:** [May 1, 2008, 9:25pm UTC](https://www.ruby-forum.com/t/please-explain-nuances-of/136398/7 "2008-05-01T21:25:46Z")
On 01.05.2008 20:54, Simon K. wrote: > > x ||= y means: x || x = y > > No, it means: x = x || y I believe you are wrong. irb(main):001:0\> h={} =\> {} irb(main):002:0\> h=Hash.new true =\> {} irb(main):003:0\> h[1] =\> true irb(main):004:0\> h[1] ||= 10 =\> true irb(main):005:0\> h =\> {} irb(main):006:0\> If you were right, h would look differently: irb(main):008:0\> h=Hash.new true =\> {} irb(main):009:0\> h[1] = h[1] || 10 =\> true irb(main):010:0\> h =\> {1=\>true} The same topic has been discussed exhaustively a few days ago. Cheers robert ---
**Author:** ![rubyfreak](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e9c0ed/32.png) [@rubyfreak](https://www.ruby-forum.com/u/rubyfreak)\ **Post date:** [May 1, 2008, 10:13pm UTC](https://www.ruby-forum.com/t/please-explain-nuances-of/136398/8 "2008-05-01T22:13:12Z")
Hi – On Fri, 2 May 2008, Simon K. wrote: > > x ||= y means: x || x = y > > No, it means: x = x || y This is becoming a bit of a perma-thread 🙂 See Robert K.'s answer, and also have a look at the blog post I mentioned in my response. It’s about exactly why x = x || y is not the right expansion for x ||= y. David ---
**Author:** ![rubyfreak](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e9c0ed/32.png) [@rubyfreak](https://www.ruby-forum.com/u/rubyfreak)\ **Post date:** [May 1, 2008, 10:39pm UTC](https://www.ruby-forum.com/t/please-explain-nuances-of/136398/9 "2008-05-01T22:39:47Z")
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 David A. Black wrote: |\> No, it means: x = x || y | | This is becoming a bit of a perma-thread 🙂 | | See Robert K.'s answer, and also have a look at the blog post I | mentioned in my response. It’s about exactly why x = x || y is not the | right expansion for x ||= y. x ||= y expands into x = x || y, since x == 1 expands to x = x + 1, and we have no reason to expect ||= to behave differently (MPLOS). Also, it works as expected if the expansion x = x || y is correct. After all: ‘The or and || operators evaluate their first operand. If true, the expression returns the value of their first operand; otherwise, the expression returns the value of the second operand.’ Programming Ruby, 2nd Edition (p. 326). And Robert’s answer works the way it works because the Hash has a default value set, which doesn’t equate to false or nil. If you override the default value by setting the value to false, the assignment works again as expected. * * * Phillip G. Twitter: [twitter.com/cynicalryan](http://twitter.com/cynicalryan) Blog: [http://justarubyist.blogspot.com](http://justarubyist.blogspot.com) Zero raised to the nth power remains zero. ~ – Pop Baslim -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.8 (MingW32) Comment: Using GnuPG with Mozilla - [http://enigmail.mozdev.org](http://enigmail.mozdev.org) iEYEARECAAYFAkgaKhoACgkQbtAgaoJTgL/LkgCeMqByMe50+mJx/j8vV3KC612p lF4AnAz+GVlTLKNPdcjZnsFbbTTwHebv =Tkje -----END PGP SIGNATURE----- ---
**Author:** ![rubyfreak](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e9c0ed/32.png) [@rubyfreak](https://www.ruby-forum.com/u/rubyfreak)\ **Post date:** [May 1, 2008, 10:43pm UTC](https://www.ruby-forum.com/t/please-explain-nuances-of/136398/10 "2008-05-01T22:43:17Z")
HI – On Fri, 2 May 2008, Phillip G. wrote: > |\>\> > | irb(main):001:0\> h={} > | > | > Quoth Joshua B.: > =\> {} > irb(main):007:0\> h[3] = h[3] || ‘not false’ > =\> “not false” The question, though, is what x ||= y expands to. Robert’s point is that if you say it expands to x = x || y, that doesn’t account for what happens with a hash that has a non-false default value. Mind you, x || x = y doesn’t account (as I mentioned) for the fact that if x isn’t defined, you can’t use that syntax. x ||= y is really its own thing, and doesn’t expand 100% of the time to anything. But x || x = y, if you allow for the undefined x thing, describes all of the behaviors, including the hash edge case. David ---
**Author:** ![rubyfreak](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e9c0ed/32.png) [@rubyfreak](https://www.ruby-forum.com/u/rubyfreak)\ **Post date:** [May 1, 2008, 10:46pm UTC](https://www.ruby-forum.com/t/please-explain-nuances-of/136398/11 "2008-05-01T22:46:49Z")
Knowing ruby the way I do, I realize that she has lots of magical surprises and I really want to get to know this girl! Happens every time! Bring a girl into the bar and a fight breaks out. ---
**Author:** ![rubyfreak](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e9c0ed/32.png) [@rubyfreak](https://www.ruby-forum.com/u/rubyfreak)\ **Post date:** [May 1, 2008, 10:26pm UTC](https://www.ruby-forum.com/t/please-explain-nuances-of/136398/12 "2008-05-01T22:26:10Z")
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Robert K. wrote: | On 01.05.2008 20:54, Simon K. wrote: |\> \* David A. Black [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) (18:56) schrieb: |\> |\>\> Hi – |\>\> |\>\> On Fri, 2 May 2008, Ruby F. wrote: |\>\> |\>\>\> I am reading some of the ruby files in rails and I an seeing the ||= |\>\>\> method used a lot. |\>\>\> knowing ruby the way I do, I realize that she has lots of magical |\>\>\> surprises and I really want to get to know this girl! |\>\> x ||= y means: x || x = y |\> |\> No, it means: x = x || y | | I believe you are wrong. | | irb(main):001:0\> h={} | =\> {} | irb(main):002:0\> h=Hash.new true | =\> {} | irb(main):003:0\> h[1] | =\> true | irb(main):004:0\> h[1] ||= 10 | =\> true | irb(main):005:0\> h | =\> {} | irb(main):006:0\> | | If you were right, h would look differently: | | irb(main):008:0\> h=Hash.new true | =\> {} | irb(main):009:0\> h[1] = h[1] || 10 | =\> true | irb(main):010:0\> h | =\> {1=\>true} | | The same topic has been discussed exhaustively a few days ago. | | Cheers | | robert | | You are wrong, too, though. I refer you to Ruby-Talk 297145[0]: Quoth Joshua B.: ‘The only reason that Chris’ example behaves like “x || x = stuff” is because he’s defined a default value for the hash. If you set a default value, than you’ll never have a keyed value be empty (i.e. nil). ’ x = x || ‘a value’ works when x is nil or false. Once the Hash has a default value, it shouldn’t be false, much less nil. See: irb(main):001:0\> h = Hash.new =\> {} irb(main):002:0\> h[1].nil? =\> true irb(main):003:0\> h[1] = h[1] || 10 =\> 10 irb(main):004:0\> h[2] = ‘not nil’ =\> “not nil” irb(main):005:0\> h[2] = h[2] || ‘a value’ =\> “not nil” irb(main):006:0\> h[3] = false =\> false irb(main):007:0\> h[3] = h[3] || ‘not false’ =\> “not false” [0] [http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/297145](http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/297145) * * * Phillip G. Twitter: [twitter.com/cynicalryan](http://twitter.com/cynicalryan) Blog: [http://justarubyist.blogspot.com](http://justarubyist.blogspot.com) ~ Calvin: I’m a genius, but I’m a misunderstood genius. Hobbes: What’s misunderstood about you? Calvin: Nobody thinks I’m a genius. – Calvin -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.8 (MingW32) Comment: Using GnuPG with Mozilla - [http://enigmail.mozdev.org](http://enigmail.mozdev.org) iEYEARECAAYFAkgaJxMACgkQbtAgaoJTgL8e0QCdHbW1PniEGPZSlC9Api4lIL7u viAAnis9nThp0JAXQEwGWU+JEM5s+ssL =3HqG -----END PGP SIGNATURE----- ---
**Author:** ![rubyfreak](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e9c0ed/32.png) [@rubyfreak](https://www.ruby-forum.com/u/rubyfreak)\ **Post date:** [May 1, 2008, 10:50pm UTC](https://www.ruby-forum.com/t/please-explain-nuances-of/136398/13 "2008-05-01T22:50:21Z")
Hi – On Fri, 2 May 2008, Phillip G. wrote: > | mentioned in my response. It’s about exactly why x = x || y is not the > | right expansion for x ||= y. > > x ||= y expands into x = x || y, since x == 1 expands to x = x + 1, and I think you mean +=. > we have no reason to expect ||= to behave differently (MPLOS). That’s really where this thread always starts, though: why doesn’t it behave like x = x || y in every case? Anyway, the thing about MPOLS is that you and I can’t invoke it 🙂 It was actually Matz who showed me the x || x = y expansion (most recently at EuRuKo, where I talked to him about it because I wanted to make sure the corrections I made to my blog post had made it correct). > the default value by setting the value to false, the assignment works > again as expected. Right, but hashes are allowed to have default values. So an explanation that accounts for that case is better than one that doesn’t. The point is that if you do a drop-in replacement x = x || y you get a different result from ||=, and with x || x = y you don’t. That means, definitively I think, that the latter is a more correct expansion. (I’m not sure how it couldn’t mean that.) Anyway, this is at least the third thread on this in recent months, and I’ve written my blog post (and correction follow-up 🙂 about it. I think I’m about ||='d out. David ---
**Author:** ![rubyfreak](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e9c0ed/32.png) [@rubyfreak](https://www.ruby-forum.com/u/rubyfreak)\ **Post date:** [May 1, 2008, 11:11pm UTC](https://www.ruby-forum.com/t/please-explain-nuances-of/136398/14 "2008-05-01T23:11:30Z")
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 David A. Black wrote: |\> x ||= y expands into x = x || y, since x == 1 expands to x = x + 1, and | | I think you mean +=. Yes, indeed. |\> we have no reason to expect ||= to behave differently (MPLOS). | | That’s really where this thread always starts, though: why doesn’t it | behave like x = x || y in every case? Anyway, the thing about MPOLS is | that you and I can’t invoke it 🙂 It was actually Matz who showed me | the x || x = y expansion (most recently at EuRuKo, where I talked to | him about it because I wanted to make sure the corrections I made to | my blog post had made it correct). It doesn’t behave that way because classes can implement and override behavior. Which can lead to surprising results, and sometimes pathological cases of Monkeypatching. 😉 Also, the MPLOS helps as a guideline, not as a hard and fast rule. 🙂 |\> And Robert’s answer works the way it works because the Hash has a |\> default value set, which doesn’t equate to false or nil. If you override |\> the default value by setting the value to false, the assignment works |\> again as expected. | | Right, but hashes are allowed to have default values. So an | explanation that accounts for that case is better than one that | doesn’t. The point is that if you do a drop-in replacement x = x || y | you get a different result from ||=, and with x || x = y you don’t. | That means, definitively I think, that the latter is a more correct | expansion. (I’m not sure how it couldn’t mean that.) However, a default value results in the Hash not evaluating to nil or false. Which is required for || and OR to use their _second_ operand (since it otherwise uses the first operand), so x || x = y cannot work. Unless we get into precedence issues here, I guess. | Anyway, this is at least the third thread on this in recent months, | and I’ve written my blog post (and correction follow-up 🙂 about it. | I think I’m about ||='d out. So am I. * * * Phillip G. Twitter: [twitter.com/cynicalryan](http://twitter.com/cynicalryan) Blog: [http://justarubyist.blogspot.com](http://justarubyist.blogspot.com) ~ Why do we drink cow’s milk? Who was the first guy who first looked at a cow and said “I think I’ll drink whatever comes out of these things when I squeeze 'em!”? – Calvin -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.8 (MingW32) Comment: Using GnuPG with Mozilla - [http://enigmail.mozdev.org](http://enigmail.mozdev.org) iEYEARECAAYFAkgaMdsACgkQbtAgaoJTgL+7ggCfZvH1Zt26JJtfKA+uPdd28oPV /28AnjWINp8XwuVrx00X2qRT/LCtz/Ny =CldW -----END PGP SIGNATURE----- ---
**Author:** ![rubyfreak](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e9c0ed/32.png) [@rubyfreak](https://www.ruby-forum.com/u/rubyfreak)\ **Post date:** [May 2, 2008, 12:00am UTC](https://www.ruby-forum.com/t/please-explain-nuances-of/136398/15 "2008-05-02T00:00:04Z")
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 David A. Black wrote: | Hi – | | On Fri, 2 May 2008, Phillip G. wrote: | | Whoops – sorry 🙂 As if. 😛 | I actually have a feeling we’re talking at cross-purposes, and that | I’m somehow not getting something. All I’m saying is that h[x] ||= | value is the same as h[x] || h[x] = value, for any hash h and any key | x. That can be demonstrated easily (as Robert did) just by | substituting one expression for the other. It’s an unusual case, but | it’s legal. I’m not sure what would be needed beyond that to | demonstrate that x = x || y is not a drop-in replacement for x ||= y. Yeah, I’m taking the Bird’s Eye View on it all, essentially saying: 'it works like this almost always, but Hash is a special case, since it has default values [or whatever the implementation detail is, that makes Hash work differently]). * * * Phillip G. Twitter: [twitter.com/cynicalryan](http://twitter.com/cynicalryan) Blog: [http://justarubyist.blogspot.com](http://justarubyist.blogspot.com) ~ “Endorsing products is the American way of expressing individuality.” - -Calvin -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.8 (MingW32) Comment: Using GnuPG with Mozilla - [http://enigmail.mozdev.org](http://enigmail.mozdev.org) iEYEARECAAYFAkgaPUgACgkQbtAgaoJTgL/kQQCggPuXLrZqT/zmBBALUKUY1/4h P44An2JhhO4GiMgkGP07DULeaV5d5a+u =nH6/ -----END PGP SIGNATURE----- ---
**Author:** ![rubyfreak](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e9c0ed/32.png) [@rubyfreak](https://www.ruby-forum.com/u/rubyfreak)\ **Post date:** [May 2, 2008, 12:11am UTC](https://www.ruby-forum.com/t/please-explain-nuances-of/136398/16 "2008-05-02T00:11:51Z")
Hi – On Fri, 2 May 2008, Phillip G. wrote: > As if. 😛 > works like this almost always, but Hash is a special case, since it has > default values [or whatever the implementation detail is, that makes > Hash work differently]). It’s possible to generalize it; someone in one of the threads wrote a class that showed the same behavior, but I can’t remember the details. I do wish it were otherwise; it’s definitely unexpected, I think. David ---
**Author:** ![rubyfreak](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e9c0ed/32.png) [@rubyfreak](https://www.ruby-forum.com/u/rubyfreak)\ **Post date:** [May 2, 2008, 12:52am UTC](https://www.ruby-forum.com/t/please-explain-nuances-of/136398/17 "2008-05-02T00:52:12Z")
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 David A. Black wrote: | Hi – | | It’s possible to generalize it; someone in one of the threads wrote a | class that showed the same behavior, but I can’t remember the details. | I do wish it were otherwise; it’s definitely unexpected, I think. Well, it is unexpected if you forget about the default value for Hash, for example. So, I agree: On first sight it _is_ unintuitive. Once you think about, though… As a tangent: I’ve just checked my copy of The Ruby Way, and its ‘Training your intuition’ sub-chapter. This gotcha isn’t part of it. ☹ Maybe it could be added for the next edition (unless Ruby 1.9/2.0 is the reason for the new edition, and the ambiguity/idiosyncrasy is removed in the new version of Ruby by then). * * * Phillip G. Twitter: [twitter.com/cynicalryan](http://twitter.com/cynicalryan) Blog: [http://justarubyist.blogspot.com](http://justarubyist.blogspot.com) ~ “Oops, I always forget the purpose of competition is to divide people into winners and losers.” -Hobbes being sarcastic -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.8 (MingW32) Comment: Using GnuPG with Mozilla - [http://enigmail.mozdev.org](http://enigmail.mozdev.org) iEYEARECAAYFAkgaSVoACgkQbtAgaoJTgL+ExwCgjbqnS7cqvvMHhPy5PRt8DX9Y nOkAoJF5YjaZuXQA71NhvdpEe/9zlFdx =sYWv -----END PGP SIGNATURE----- ---
**Author:** ![rubyfreak](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e9c0ed/32.png) [@rubyfreak](https://www.ruby-forum.com/u/rubyfreak)\ **Post date:** [May 2, 2008, 12:59am UTC](https://www.ruby-forum.com/t/please-explain-nuances-of/136398/18 "2008-05-02T00:59:14Z")
2008/5/2 Ruby F. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid): ---
**Author:** ![rubyfreak](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e9c0ed/32.png) [@rubyfreak](https://www.ruby-forum.com/u/rubyfreak)\ **Post date:** [May 2, 2008, 1:00am UTC](https://www.ruby-forum.com/t/please-explain-nuances-of/136398/19 "2008-05-02T01:00:24Z")
David A. Black wrote: > It’s possible to generalize it; someone in one of the threads wrote a > class that showed the same behavior, but I can’t remember the details. [http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/297185](http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/297185) ---
**Author:** ![rubyfreak](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e9c0ed/32.png) [@rubyfreak](https://www.ruby-forum.com/u/rubyfreak)\ **Post date:** [May 1, 2008, 11:28pm UTC](https://www.ruby-forum.com/t/please-explain-nuances-of/136398/20 "2008-05-01T23:28:27Z")
Hi – On Fri, 2 May 2008, Phillip G. wrote: > However, a default value results in the Hash not evaluating to nil or > false. Which is required for || and OR to use their _second_ operand > (since it otherwise uses the first operand), so x || x = y cannot work. > Unless we get into precedence issues here, I guess. It depends what you mean by work 🙂 See Robert’s example. > | Anyway, this is at least the third thread on this in recent months, > | and I’ve written my blog post (and correction follow-up 🙂 about it. > | I think I’m about ||='d out. > > So am I. Whoops – sorry 🙂 I actually have a feeling we’re talking at cross-purposes, and that I’m somehow not getting something. All I’m saying is that h[x] ||= value is the same as h[x] || h[x] = value, for any hash h and any key x. That can be demonstrated easily (as Robert did) just by substituting one expression for the other. It’s an unusual case, but it’s legal. I’m not sure what would be needed beyond that to demonstrate that x = x || y is not a drop-in replacement for x ||= y. David [Next page](https://www.ruby-forum.com/t/please-explain-nuances-of/136398.md?page=2)