# Scope of an @variable **URL:** \ **Category:** Ruby\ **Created:** [March 14, 2006, 11:01pm UTC](https://www.ruby-forum.com/t/scope-of-an-variable/54876 "2006-03-14T23:01:56Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![nko](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/n/91b2a8/32.png) [@nko](https://www.ruby-forum.com/u/nko)\ **Post date:** [March 14, 2006, 11:01pm UTC](https://www.ruby-forum.com/t/scope-of-an-variable/54876/1 "2006-03-14T23:01:56Z")
I’ve got a class. I want some methods of this class to be able to edit some data that’s “global” within any given instance of this class. For example: class Person @name def changeName(newName) @name = newName end def sayName() puts "My name is " + @name end end It seems that @name reverts back once I leave the scope of any method that manipulates it. ---
**Author:** ![nko](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/n/91b2a8/32.png) [@nko](https://www.ruby-forum.com/u/nko)\ **Post date:** [March 14, 2006, 11:08pm UTC](https://www.ruby-forum.com/t/scope-of-an-variable/54876/2 "2006-03-14T23:08:41Z")
you need to use @@name. ---
**Author:** ![nko](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/n/91b2a8/32.png) [@nko](https://www.ruby-forum.com/u/nko)\ **Post date:** [March 14, 2006, 11:17pm UTC](https://www.ruby-forum.com/t/scope-of-an-variable/54876/3 "2006-03-14T23:17:49Z")
Adam S. wrote: > you need to use @@name. I was under the impression (newbie alert) that @name was for instances and @@name was for classes as a whole (ie, @@ variables change that value in all instances of Class). Is there a way to have variables that apply to all instances of a Class? ---
**Author:** ![nko](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/n/91b2a8/32.png) [@nko](https://www.ruby-forum.com/u/nko)\ **Post date:** [March 15, 2006, 3:13am UTC](https://www.ruby-forum.com/t/scope-of-an-variable/54876/4 "2006-03-15T03:13:47Z")
Hi – On Wed, 15 Mar 2006, Nathan O. wrote: > end > > def sayName() > puts "My name is " + @name > end > end > > It seems that @name reverts back once I leave the scope of any method > that manipulates it. As you’ve learned from some of the other responses, @name is an instance variable. Each instance variable belongs to one object. You can always tell _which_ object: it’s whatever the default object (self) is, at the point where the “@var” is executed. Note that self changes between a class definition and an instance method definition: class Person puts self def some\_method puts self end end Person.new.some\_method This code will give you: Person #Person:0x352814 In the top level of the class definition, self is the actual class object (Person), but inside an instance method, it’s the instance (indicated by the #\ expression). So… @name in the outer scope is actually an instance variable belonging to the class object, while inside any instance method, @name is an instance variable belonging to the instance. The two @name’s have no connection to each other at all. You can use class variables to get a variable that can be seen in both scopes, but if you’ve got a property like “name” and you find yourself manipulating it outside of any instance method, something’s probably in need of tweaking in the program design (since the name of any particular instance shouldn’t be of concern at the class level). David – David A. Black (removed\_email\_address@domain.invalid) Ruby Power and Light, LLC ([http://www.rubypowerandlight.com](http://www.rubypowerandlight.com)) “Ruby for Rails” chapters now available from Manning Early Access Program! [Ruby for Rails](http://www.manning.com/books/black) ---
**Author:** ![nko](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/n/91b2a8/32.png) [@nko](https://www.ruby-forum.com/u/nko)\ **Post date:** [March 15, 2006, 3:19am UTC](https://www.ruby-forum.com/t/scope-of-an-variable/54876/5 "2006-03-15T03:19:50Z")
removed\_email\_address@domain.invalid wrote: > Note that self changes between a class definition and an instance > method definition: Light bulbs floating above list readers’ heads around the world just illuminated. Thanks for the great explanation! –Steve ---
**Author:** ![nko](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/n/91b2a8/32.png) [@nko](https://www.ruby-forum.com/u/nko)\ **Post date:** [March 14, 2006, 11:39pm UTC](https://www.ruby-forum.com/t/scope-of-an-variable/54876/6 "2006-03-14T23:39:28Z")
On Mar 14, 2006, at 11:18 PM, Nathan O. wrote: > I was under the impression (newbie alert) that @name was for instances > and @@name was for classes as a whole (ie, @@ variables change that > value in all instances of Class). Is there a way to have variables > that > apply to all instances of a Class? Use an initialize method: class Person def initialize(name=“Anonymous”) @name = name end attr\_accessor :name def to\_s “My name is #{@name}” end end person = Person.new puts person # → My name is Anonymous person.name = “Fred” puts person # → My name is Fred This should help you: [Programming Ruby: The Pragmatic Programmer's Guide](http://ruby-doc.org/docs/ProgrammingRuby) – Daniel ---
**Author:** ![nko](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/n/91b2a8/32.png) [@nko](https://www.ruby-forum.com/u/nko)\ **Post date:** [March 15, 2006, 8:52pm UTC](https://www.ruby-forum.com/t/scope-of-an-variable/54876/7 "2006-03-15T20:52:31Z")
On 3/14/06, Nathan O. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > Adam S. wrote: > > > you need to use @@name. > > I was under the impression (newbie alert) that @name was for instances > and @@name was for classes as a whole (ie, @@ variables change that > value in all instances of Class). Is there a way to have variables that > apply to all instances of a Class? Oops, I read the question too quickly. Sorry. David Black has the right explanation. -Adam