require 'memoist'

class A
  extend Memoist

  def foo
    puts 'A'
  end

  memoize :foo
end

class B < A
  def foo
    puts 'B'
  end
end

class C < A
  def foo
    puts 'C'
  end

  memoize :foo
end

class D < A
 def foo
    puts 'D'
  end

  memoize :foo, identifier: :d_foo
end

a = A.new
a.foo
a.foo

b = B.new
b.foo
b.foo

c = C.new
c.foo
c.foo

d = D.new
d.foo
d.foo