gistfile1.rb

#if I have...

A.new(B.new(C.new(D.new)))

#is there some way (some inject sorcery?) to construct this from a list of the classes?

list = [A, B, C, D]

Maybe something like this?

def recursive_new(list)
  cls = list.shift
  cls.new(recursive_new(list)) if cls
end

class X
  def initialize(other)
    @other = other
  end
end

class A < X; end
class B < X; end
class C < X; end
class D < X; end

[ A, B, C, D ].reverse.inject { |acc, klass| klass.new(acc) }

I finally settled on

[A, B, C].reverse.inject(D.new) {|acc, klass| klass.new(acc) }

Which is obviously cheating, but whatever.