Question

I see that Ruby has the following variables:
– global variables (represented by $variable_name)
– class variables (represented by @@variable_name)
– instance variables (represented by @variable_name) and
– local variables (represented by variable_name or _variable_name)

Occasionally I see the following in the rails source code:

class SomeClass
@var
end

Here what exactly @var represent and what do you call it, metaclass variable?
Also whats the advantage of using this kind of variables?

Answer 1

It is one of the classes instance variables. In Ruby, everything is an object, even classes, so it isn’t surprising that classes can have instance variables.

class A
  @@class_var = 1
  @instance_var = 1
end
A.class_variables
#=> ["@@class_var"]
A.instance_variables
#=>["@instance_var"]

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