# | versus || Any reason for this issue? **URL:** \ **Category:** ruby-talk\ **Created:** [2 May 2008 14:01 UTC](https://rubytalk.org/t/versus-any-reason-for-this-issue/46250 "2008-05-02T14:01:32Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![Inaki\_Baz\_Castillo](https://avatars.discourse-cdn.com/v4/letter/i/f14d63/32.png) [@Inaki\_Baz\_Castillo](https://rubytalk.org/u/Inaki_Baz_Castillo)\ **Post date:** [2 May 2008 14:01 UTC](https://rubytalk.org/t/versus-any-reason-for-this-issue/46250/1 "2008-05-02T14:01:32Z")
Hi, why in the second case the non declared "my\_var" variable is processed but not in the first case? > nil || 2 || my\_var =\> 2 > nil | 2 | my\_var NameError: undefined local variable or method `my\_var' Of course, I prefer the first case: 2 is already true so there is no reason to read the next "my\_var". Also, it's not good for performance, is it? > **···** > > -- > Iñaki Baz Castillo > \ ---
**Author:** ![David\_A\_Black1](https://avatars.discourse-cdn.com/v4/letter/d/bcef8e/32.png) [@David\_A\_Black1](https://rubytalk.org/u/David_A_Black1)\ **Post date:** [2 May 2008 14:13 UTC](https://rubytalk.org/t/versus-any-reason-for-this-issue/46250/2 "2008-05-02T14:13:52Z")
Hi -- > Hi, why in the second case the non declared "my\_var" variable is > processed but not in the first case? > > \> nil || 2 || my\_var > =\> 2 > > \> nil | 2 | my\_var > NameError: undefined local variable or method `my\_var' > > Of course, I prefer the first case: 2 is already true so there is no > reason to read the next "my\_var". Also, it's not good for performance, > is it? The single bar and the double bar are not related. | is a method that any class or object can define. For example, Fixnums use it as a bitwise operator:    4 | 1 # 5 (i.e., 100 | 001 == 101) The single bar doesn't short circuit, whereas the || operator does.    nil || 2 || 1/0 # 2 (it never reaches 1/0 so doesn't blow up) If you do nil || my\_var, my\_var will be reached and will give you an error if it isn't defined. David > **···** > > On Fri, 2 May 2008, Iñaki Baz Castillo wrote: > > -- > Rails training from David A. Black and Ruby Power and Light: >    INTRO TO RAILS June 9-12 Berlin >    ADVANCING WITH RAILS June 16-19 Berlin >    INTRO TO RAILS June 24-27 London (Skills Matter) > See [http://www.rubypal.com](http://www.rubypal.com) for details and updates! ---
**Author:** ![Florian\_Gilcher](https://avatars.discourse-cdn.com/v4/letter/f/57b2e6/32.png) [@Florian\_Gilcher](https://rubytalk.org/u/Florian_Gilcher)\ **Post date:** [2 May 2008 14:15 UTC](https://rubytalk.org/t/versus-any-reason-for-this-issue/46250/3 "2008-05-02T14:15:30Z")
to evaluate both Operands while the value of a logical OR (||) is known at the moment that one of the Operands is true. Regards Florian Gilcher > **···** > > On May 2, 2008, at 4:01 PM, Iñaki Baz Castillo wrote: > > > Hi, why in the second case the non declared "my\_var" variable is > > processed but not in the first case? > > > > \> nil || 2 || my\_var > > =\> 2 > > > > \> nil | 2 | my\_var > > NameError: undefined local variable or method `my\_var' > > > > Of course, I prefer the first case: 2 is already true so there is no > > reason to read the next "my\_var". Also, it's not good for performance, > > is it? > > > is the bitwise OR and something entirely different from ||. | needs ---
**Author:** ![Robert\_K1](https://yyz1.discourse-cdn.com/flex029/user_avatar/rubytalk.org/robert_k1/32/1830_2.png) [@Robert\_K1](https://rubytalk.org/u/Robert_K1)\ **Post date:** [2 May 2008 14:20 UTC](https://rubytalk.org/t/versus-any-reason-for-this-issue/46250/4 "2008-05-02T14:20:07Z")
> Hi, why in the second case the non declared "my\_var" variable is > processed but not in the first case? Because || does short circuit while | does not. > \> nil || 2 || my\_var > =\> 2 > > \> nil | 2 | my\_var > NameError: undefined local variable or method `my\_var' > > Of course, I prefer the first case: 2 is already true so there is no > reason to read the next "my\_var". Also, it's not good for performance, > is it? "||" is the short circuit boolean "or" operator. You cannot override it. "|" on the other hand is an operator that can be overloaded and it does not short circuit. It would not make any sense to make "|" short circuit because it can contain arbitrary functionality. Here are some classes that implement "|": $ ruby -e 'ObjectSpace.each\_object(Module) {|cl| p cl if cl.instance\_methods.include? "|"}' Array Bignum Fixnum FalseClass TrueClass NilClass Kind regards   robert > **···** > > On 02.05.2008 16:01, Iñaki Baz Castillo wrote: ---
**Author:** ![Inaki\_Baz\_Castillo](https://avatars.discourse-cdn.com/v4/letter/i/f14d63/32.png) [@Inaki\_Baz\_Castillo](https://rubytalk.org/u/Inaki_Baz_Castillo)\ **Post date:** [2 May 2008 14:25 UTC](https://rubytalk.org/t/versus-any-reason-for-this-issue/46250/5 "2008-05-02T14:25:55Z")
Thanks to all for those excellent explanations 🙂 > **···** > > 2008/5/2, Robert Klemme \: > > > On 02.05.2008 16:01, Iñaki Baz Castillo wrote: > > > > \> Hi, why in the second case the non declared "my\_var" variable is > > \> processed but not in the first case? > > \> > > > > Because || does short circuit while | does not. > > > > \> \> nil || 2 || my\_var > > \> =\> 2 > > \> > > \> \> nil | 2 | my\_var > > \> NameError: undefined local variable or method `my\_var' > > \> > > \> Of course, I prefer the first case: 2 is already true so there is no > > \> reason to read the next "my\_var". Also, it's not good for performance, > > \> is it? > > \> > > > > "||" is the short circuit boolean "or" operator. You cannot override it. > > "|" on the other hand is an operator that can be overloaded and it does not > > short circuit. It would not make any sense to make "|" short circuit > > because it can contain arbitrary functionality. > > > > Here are some classes that implement "|": > > > > $ ruby -e 'ObjectSpace.each\_object(Module) {|cl| p cl if > > cl.instance\_methods.include? "|"}' > > Array > > Bignum > > Fixnum > > FalseClass > > TrueClass > > NilClass > > -- > Iñaki Baz Castillo > \ ---
**Author:** ![Robert\_K1](https://yyz1.discourse-cdn.com/flex029/user_avatar/rubytalk.org/robert_k1/32/1830_2.png) [@Robert\_K1](https://rubytalk.org/u/Robert_K1)\ **Post date:** [2 May 2008 14:35 UTC](https://rubytalk.org/t/versus-any-reason-for-this-issue/46250/6 "2008-05-02T14:35:04Z")
This is only mostly correct. Semantics of | depend on the class that implements it. irb(main):001:0\> %w{a b c} | %w{c d e} =\> ["a", "b", "c", "d", "e"] irb(main):002:0\> %w{a b c} & %w{c d e} =\> ["c"] Cheers   robert > **···** > > On 02.05.2008 16:15, Florian Gilcher wrote: > > > -----BEGIN PGP SIGNED MESSAGE----- > > Hash: SHA1 > > > > On May 2, 2008, at 4:01 PM, Iñaki Baz Castillo wrote: > > > > > Hi, why in the second case the non declared "my\_var" variable is > > > processed but not in the first case? > > > > > > \> nil || 2 || my\_var > > > =\> 2 > > > > > > \> nil | 2 | my\_var > > > NameError: undefined local variable or method `my\_var' > > > > > > Of course, I prefer the first case: 2 is already true so there is no > > > reason to read the next "my\_var". Also, it's not good for performance, > > > is it? > > > > \> is the bitwise OR and something entirely different from ||.