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Re: Understanding global variables.

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Fily Salas wrote in post #992901:
> Hi,
>
> I thought that I understood the different type of variables in Ruby but
> now that I'm actually trying them I see that I didn't, reading is easy
> putting things in practice is hard.
>
> class Car
>   @mil_gal = 30
>   @fuel_gal = 10
>
>   def go(mil_gal, fuel_gal)
>     @mil_gal = mil_gal
>     @fuel_gal=fuel_gal
>      millage =@mil_gal * @fuel_gal
>      puts millage
>   end
> end
>
> car = Car.new
> car.go(10,50)
>
> In the above code I have two global variables @mil_gal = 30 and
> @fuel_gal = 10,

Wrong.  In ruby, global variables start with a $ sign and they are 
visible everywhere(that is except for the regex 'global' variables that 
ruby predefines)

> well let me rephrase this in my eyes they are global
> variables...

You may think those variables are global to the class, i.e. they can be 
referred to in any method definition--but they cannot.  "Instance 
variables", the ones that start with '@' attach themselves to whatever 
object is self at the time they are created, and inside a class 
definition but outside of any method definitions self is equal to the 
class:

class A
  puts self
end

--output:--
A

In your case, the instance variables attach to the class, and therefore 
you must use the class as the receiver:

Car.mil_gal

Those are known as "class instance variables" and are preferred over 
class variables, e.g. @@mil_gal.

A variable that is visible in all method definitions within a class is 
called an "instance variable", and it begins with "@" and can be created 
inside a method definition to get the behaviour you want. Inside a 
method definition, self is equal to the object that called the method, 
so the instance variable attaches to the object.

In ruby, classes carry the common methods of all instances of the class, 
and instances each have their own instance variables.

-- 
Posted via http://www.ruby-forum.com/.

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Thread

Understanding global variables. Fily Salas <fs_tigre@hotmail.com> - 2011-04-14 19:55 -0500
  Re: Understanding global variables. 7stud -- <bbxx789_05ss@yahoo.com> - 2011-04-14 20:05 -0500
  Re: Understanding global variables. jake kaiden <jakekaiden@yahoo.com> - 2011-04-14 22:30 -0500
  Re: Understanding global variables. Fily Salas <fs_tigre@hotmail.com> - 2011-04-15 08:13 -0500
    Re: Understanding global variables. 7stud -- <bbxx789_05ss@yahoo.com> - 2011-04-15 13:10 -0500
  Re: Understanding global variables. jake kaiden <jakekaiden@yahoo.com> - 2011-04-15 08:36 -0500
  Re: Understanding global variables. Fily Salas <fs_tigre@hotmail.com> - 2011-04-15 09:14 -0500
  Re: Understanding global variables. jake kaiden <jakekaiden@yahoo.com> - 2011-04-15 09:20 -0500
  Re: Understanding global variables. Fily Salas <fs_tigre@hotmail.com> - 2011-04-16 14:47 -0500

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