Class variables (available to whole inheritance tree) and class instance variables (private to the class) in Ruby can be confusing:
```ruby
class Foo
@@cls_var = 'foo'
@cls_instvar = 'foo'
def test
p "instance:"
p " class variable: #{@@cls_var}"
p " class instance variable: #{@cls_instvar}"
end
def self.test
p "class:"
p " class variable: #{@@cls_var}"
p " class instance variable: #{@cls_instvar}"
end
end
class Bar < Foo
@@cls_var = 'bar'
@cls_instvar = 'bar'
end
f = Foo.new
p "------------"
p "Foo"
p "------------"
f.test
p "~~~~~~~~~~~~"
Foo.test
p "------------"
p "Bar"
p "------------"
b = Bar.new
b.test
p "~~~~~~~~~~~~"
Bar.test
```
Output is:
```ruby
------------
Foo
------------
instance:
class variable: bar
class instance variable:
~~~~~~~~~~~~
class:
class variable: bar
class instance variable: foo
------------
Bar
------------
instance:
class variable: bar
class instance variable:
~~~~~~~~~~~~
class:
class variable: bar
class instance variable: bar
```