# Are these the same? **URL:** \ **Category:** ruby-talk\ **Created:** [14 June 2005 00:05 UTC](https://rubytalk.org/t/are-these-the-same/18958 "2005-06-14T00:05:30Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![Lowell\_Kirsh](https://avatars.discourse-cdn.com/v4/letter/l/ed8c4c/32.png) [@Lowell\_Kirsh](https://rubytalk.org/u/Lowell_Kirsh)\ **Post date:** [14 June 2005 00:05 UTC](https://rubytalk.org/t/are-these-the-same/18958/1 "2005-06-14T00:05:30Z")
I'm wondering about the difference between writing something like @x = ... and self.x = ... from within a class. Are they the same thing? To be more concrete, I have given a fuller example below: class Foo    def bar      self.x = 1    end end class Foo    def bar      @x = 1    end end Lowell ---
**Author:** ![Joel\_VanderWerf1](https://avatars.discourse-cdn.com/v4/letter/j/94ad74/32.png) [@Joel\_VanderWerf1](https://rubytalk.org/u/Joel_VanderWerf1)\ **Post date:** [14 June 2005 00:32 UTC](https://rubytalk.org/t/are-these-the-same/18958/2 "2005-06-14T00:32:40Z")
Lowell Kirsh wrote: > I'm wondering about the difference between writing something like > > @x = ... > and > self.x = ... > > from within a class. Are they the same thing? To be more concrete, I have given a fuller example below: They are different, but the degree of difference depends on the context. The "@x =" construct is ruby's built-in way of assigning to an instance variable in the current object ("self"). It does not invoke any methods. The "self.x =" construct is a special syntax for calling the method whose name is "x=" on the object denoted by "self". This method may or may not assign to the instance variable @x, and it may do other things in addition to assigning to @x. For instance, you might also execute some debugging code: class Foo    def x=(val)      puts "setting x = #{val.inspect}"      @x = val    end end Or you might not assign to @x at all. For example: class Square    def width=(val)      self.height = val    end    def height=(val)      @height = val    end end Since width and height must be equal, there's no need to store them separately. But users of the Square class don't have to know that. Some people call this the "uniform access principle". ---
**Author:** ![HAL\_9000](https://avatars.discourse-cdn.com/v4/letter/h/90ced4/32.png) [@HAL\_9000](https://rubytalk.org/u/HAL_9000)\ **Post date:** [14 June 2005 00:38 UTC](https://rubytalk.org/t/are-these-the-same/18958/3 "2005-06-14T00:38:10Z")
Lowell Kirsh wrote: > I'm wondering about the difference between writing something like > > @x = ... > and > self.x = ... > > from within a class. Are they the same thing? Not necessarily the same. @x = ... # assigns an instance variable self.x = ... # invokes a method called x= (which doesn't                 # exist in your example. Now, having said they're different... if you add    attr\_accessor :x then they are more the same. Bear in mind that instance variables are accessed from the "outside world" only via methods. And when you say self.x within a class, you are basically accessing it "from the outside" even though you are inside the class (dumb analogy: You're in your house, and you reach outside a window and then reach into the window next to it "from outside"). Also bear in mind that if you (manually) define a method x=, you \*could\* define it in a stupid or misleading way (just as you \*could\* give misleading names to all your variables and methods):      def x=(val)        puts "Ha, fooled you! I'm setting @y to 123!"        @y = 123 # and not even using val      end Hope this helps... Hal ---
**Author:** ![Lowell\_Kirsh](https://avatars.discourse-cdn.com/v4/letter/l/ed8c4c/32.png) [@Lowell\_Kirsh](https://rubytalk.org/u/Lowell_Kirsh)\ **Post date:** [14 June 2005 04:15 UTC](https://rubytalk.org/t/are-these-the-same/18958/4 "2005-06-14T04:15:30Z")
Thank you both. Things are much clearer now 🙂 Lowell Kirsh wrote: > **···** > > > I'm wondering about the difference between writing something like > > > > @x = ... > > and > > self.x = ... > > > > from within a class. Are they the same thing? To be more concrete, I have given a fuller example below: > > > > class Foo > >   def bar > >     self.x = 1 > >   end > > end > > > > class Foo > >   def bar > >     @x = 1 > >   end > > end > > > > Lowell