# Problem with 'self'. behaves different on setting and gettin **URL:** \ **Category:** ruby-talk\ **Created:** [30 November 2007 13:45 UTC](https://rubytalk.org/t/problem-with-self-behaves-different-on-setting-and-gettin/42634 "2007-11-30T13:45:38Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![Michal\_Gabrukiewicz](https://avatars.discourse-cdn.com/v4/letter/m/c57346/32.png) [@Michal\_Gabrukiewicz](https://rubytalk.org/u/Michal_Gabrukiewicz)\ **Post date:** [30 November 2007 13:45 UTC](https://rubytalk.org/t/problem-with-self-behaves-different-on-setting-and-gettin/42634/1 "2007-11-30T13:45:38Z")
hello, i have a question according 'self'. I have setup a small simple scenario to simulate the problem. This following small program works fine .. > class User >   def set\_foo >     self.x = '1' >   end >   def get\_foo >     x >   end >   def x=(val) >     @x = val >   end >   def x >     @x >   end > end > > u = User.new > u.set\_foo > puts(u.x) > puts(u.get\_foo) when i now remove the 'self' within the method 'set\_foo' it does not set the values any more. > class User >   def set\_foo >     x = '1' >   end >   def get\_foo >     x >   end >   def x=(val) >     @x = val >   end >   def x >     @x >   end > end > > u = User.new > u.set\_foo > puts(u.x) > puts(u.get\_foo) so my 1st question is: why doesnt the 'set\_foo' method calls the 'x' method if i remove the self? THE INTERESTING THING: 'get\_foo' works with 'x' and 'self.x' and the 2nd question: when should i use self now and when not and why is there this strange behavoir? thanks for looking into this. > **路路路** > > -- > Posted via [http://www.ruby-forum.com/\](http://www.ruby-forum.com/%5C). ---
**Author:** ![Jari\_Williamsson](https://avatars.discourse-cdn.com/v4/letter/j/c4cdca/32.png) [@Jari\_Williamsson](https://rubytalk.org/u/Jari_Williamsson)\ **Post date:** [30 November 2007 14:33 UTC](https://rubytalk.org/t/problem-with-self-behaves-different-on-setting-and-gettin/42634/2 "2007-11-30T14:33:48Z")
Michal Gabrukiewicz wrote: > so my 1st question is: why doesnt the 'set\_foo' method calls the 'x' > method if i remove the self? Because it now thinks that x is a local variable. This is one of the basics of Ruby. If you use NetBeans, the editor will alert you about these kind of things in the colored syntax. > THE INTERESTING THING: 'get\_foo' works with 'x' and 'self.x' Yes, but with different result behind the scenes. 'x' is the same as 'x()', while 'self.x' is the same a '@x' > and the 2nd question: when should i use self now and when not and why is > there this strange behavoir? You should use self when a left-side argument can be interpreted as a local variable. Best regards, Jari Williamsson ---
**Author:** ![Michal\_Gabrukiewicz](https://avatars.discourse-cdn.com/v4/letter/m/c57346/32.png) [@Michal\_Gabrukiewicz](https://rubytalk.org/u/Michal_Gabrukiewicz)\ **Post date:** [30 November 2007 15:04 UTC](https://rubytalk.org/t/problem-with-self-behaves-different-on-setting-and-gettin/42634/3 "2007-11-30T15:04:10Z")
thanks jari ... i can see clearly now 馃檪 Jari Williamsson wrote: > Michal Gabrukiewicz wrote: > > > so my 1st question is: why doesnt the 'set\_foo' method calls the 'x' > > method if i remove the self? > > Because it now thinks that x is a local variable. This is one of the > basics of Ruby. thats the important thing! > **路路路** > > > If you use NetBeans, the editor will alert you about these kind of > > things in the colored syntax. > > > > > THE INTERESTING THING: 'get\_foo' works with 'x' and 'self.x' > > > > Yes, but with different result behind the scenes. 'x' is the same as > > 'x()', while 'self.x' is the same a '@x' > > > > > and the 2nd question: when should i use self now and when not and why is > > > there this strange behavoir? > > > > You should use self when a left-side argument can be interpreted as a > > local variable. > > > > Best regards, > > > > Jari Williamsson > > -- > Posted via [http://www.ruby-forum.com/\](http://www.ruby-forum.com/%5C). ---
**Author:** ![HiddenBek](https://avatars.discourse-cdn.com/v4/letter/h/bc79bd/32.png) [@HiddenBek](https://rubytalk.org/u/HiddenBek)\ **Post date:** [30 November 2007 15:15 UTC](https://rubytalk.org/t/problem-with-self-behaves-different-on-setting-and-gettin/42634/4 "2007-11-30T15:15:02Z")
Here's a small example to illustrate Jari's point: class User   attr\_accessor :x   def foo     self.x = 1     puts x # =\> 1     x = 2     puts x # =\> 2     puts self.x # =\> 1   end end User.new.foo Any assignment without an explicit receiver will set a local variable. You also need to use self if the method you're calling is shadowed by a local variable with the same name, as in my example above. Finally, you must use self if the method you're calling is a reserved word, such as self.class. Page 86 of the Pickaxe book (Programming Ruby) talks about this. > **路路路** > > On Nov 30, 10:33 am, Jari Williamsson \ wrote: > > > Michal Gabrukiewicz wrote: > > \> so my 1st question is: why doesnt the 'set\_foo' method calls the 'x' > > \> method if i remove the self? > > > > Because it now thinks that x is a local variable. This is one of the > > basics of Ruby. > > > > If you use NetBeans, the editor will alert you about these kind of > > things in the colored syntax. > > > > \> THE INTERESTING THING: 'get\_foo' works with 'x' and 'self.x' > > > > Yes, but with different result behind the scenes. 'x' is the same as > > 'x()', while 'self.x' is the same a '@x' > > > > \> and the 2nd question: when should i use self now and when not and why is > > \> there this strange behavoir? > > > > You should use self when a left-side argument can be interpreted as a > > local variable. > > > > Best regards, > > > > Jari Williamsson ---
**Author:** ![Claudio\_Caseiro](https://avatars.discourse-cdn.com/v4/letter/c/ecccb3/32.png) [@Claudio\_Caseiro](https://rubytalk.org/u/Claudio_Caseiro)\ **Post date:** [30 November 2007 15:40 UTC](https://rubytalk.org/t/problem-with-self-behaves-different-on-setting-and-gettin/42634/5 "2007-11-30T15:40:30Z")
Jari Williamsson wrote: > Michal Gabrukiewicz wrote: > > > THE INTERESTING THING: 'get\_foo' works with 'x' and 'self.x' > > Yes, but with different result behind the scenes. 'x' is the same as > 'x()', while 'self.x' is the same a '@x' I think this is not correct. Since there are no local variable "x" in method get\_foo, bot "x" and "self.x" will send message x to self. If you reopen class User: class User   def x     "2"   end end Both x and self.x in get\_foo will return "2", even if @x is "1" Regards, > **路路路** > > -- > Cl谩udio Caseiro > > -- > Posted via [http://www.ruby-forum.com/\](http://www.ruby-forum.com/%5C). ---
**Author:** ![Daniel\_Martin](https://avatars.discourse-cdn.com/v4/letter/d/dc4da7/32.png) [@Daniel\_Martin](https://rubytalk.org/u/Daniel_Martin)\ **Post date:** [1 December 2007 22:05 UTC](https://rubytalk.org/t/problem-with-self-behaves-different-on-setting-and-gettin/42634/6 "2007-12-01T22:05:39Z")
One minor correction to an otherwise perfectly fine explanation: Jari Williamsson \ writes: > Yes, but with different result behind the scenes. 'x' is the same as > 'x()', while 'self.x' is the same a '@x' Not quite. self.x is the same as x(), but: self.x = ... is the same as self.x=(...). The connection to @x only happens because of the definition for the x= method in the orginal post. > **路路路** > > -- > s=%q( Daniel Martin -- martin@snowplow.org >        puts "s=%q(#{s})",s.to\_a.last ) >        puts "s=%q(#{s})",s.to\_a.last ---
**Author:** ![Charles\_Oliver\_Nutte](https://avatars.discourse-cdn.com/v4/letter/c/71e660/32.png) [@Charles\_Oliver\_Nutte](https://rubytalk.org/u/Charles_Oliver_Nutte)\ **Post date:** [30 November 2007 15:47 UTC](https://rubytalk.org/t/problem-with-self-behaves-different-on-setting-and-gettin/42634/7 "2007-11-30T15:47:09Z")
Cl谩udio Caseiro wrote: > Jari Williamsson wrote: > > > Michal Gabrukiewicz wrote: > > > > > THE INTERESTING THING: 'get\_foo' works with 'x' and 'self.x' > > > > Yes, but with different result behind the scenes. 'x' is the same as > > 'x()', while 'self.x' is the same a '@x' > > I think this is not correct. Since there are no local variable "x" in method get\_foo, bot "x" and "self.x" will send message x to self. > > If you reopen class User: > > class User >   def x >     "2" >   end > end > > Both x and self.x in get\_foo will return "2", even if @x is "1" You are correct. Both are calls to the "x" method. The only difference is that "self.x" will fail if "x" is private. - Charlie