Question: So suppose I have this (not working): 

```
class User
   description = "I am User class variable"
   def print
       puts description
   end
end

```

So, how should I use the var description, how to pass this into a method as a default parameter, or used in the method directly? Thanks..

Answer: 
To define a class variable, use an `@@`:

```
class User
   @@description = "I am a User class variable"

   def print
       puts @@description
   end
end

```
Instance variables must be prefixed with an **@** and are not accessible from outside.
Class variables must be prefixed with an **@@**.

The first time you use this variable anywhere in code, it will be initialized.
If you want to access the value from outside:

```
attr_reader :description

```

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