Understanding Variables

Anton_S

In classes:
@var - instance variable
@@var - class variable

If those variables would be initialized outside of class(Ex: Sketchy physics ontick attribute: "if frame==0 then @var=0; @@var=0; end"), would there be no difference between those variables anymore?

Thanks, ant-on

Dan Rathbun

@anton_s said:

If those variables would be initialized outside of class...

Your question makes no sense at all.

A class variable, by it's nature, is WITHIN a class, and accessible to all instances of that class. It's like a family value, as opposed to a personal (instance var) value or community (global var) value.

An instance var (@var) is like a personal value. (Thinking of yourself as an instance of class Human,.... how much money YOU have in YOUR pocket, is an instance value.)

How much money ALL of us humans together have in our pockets, would be a class value.

And... DONT create @var instance variables, in the global ObjectSpace (at least in plugins that you distribute.)

Now logically, if your set them both to point at 0, and test them with ==, you will get a true result, but only for as long as they point at the same object. (Remember in Ruby, the set of Integers is "immediate", meaning their is only 1 of each ordinal in the set. EVER.)

OK? There are NOT two variables, each holding a value of 0.
There ARE two references, each pointing at the same Ruby object, 0 which is an instance of class Integer, and the only one in the set that equals zero, numerically.

Ruby has 2 things. Objects and References that point at objects.

If you keep thinking "variables" instead of "references", your will just frustrate yourself.
@var = 8
"The reference @var shall point at the object 8."
@@var = @var
"The reference @@var shall point at the object that @var is pointing at."
@var = 32
"The reference @var shall be reassigned to point at the object 32."
In the console:
@var

32
@@var
8

Anton_S

Okay, now I know!! And yeah at first my question made sense to me, but now it doesn't!

Thanks