cvars_ivars.rb

class Foo
  @@foo = nil
  def self.seti( value )
    @foo = value
  end
  def self.setc( value )
    @@foo = value
  end
  def self.geti
    @foo
  end
  def self.getc
    @@foo
  end
end

class Bar < Foo
end

p [ Foo.geti, Bar.geti, Foo.getc, Bar.getc ]
#=> [nil, nil, nil, nil]

Foo.seti :foo_i
Foo.setc :foo_c

p [ Foo.geti, Bar.geti, Foo.getc, Bar.getc ]
#=> [:foo_i, nil, :foo_c, :foo_c]

Bar.seti :bar_i
Bar.setc :bar_c

p [ Foo.geti, Bar.geti, Foo.getc, Bar.getc ]
#=> [:foo_i, :bar_i, :bar_c, :bar_c]