Hi --

On Wed, 15 Mar 2006, Nathan Olberding wrote:

> 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.

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 #<Person...> 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 (dblack / wobblini.net)
Ruby Power and Light, LLC (http://www.rubypowerandlight.com)

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