Playing with chaining #then on a Swift-like Optional

optional.rb

# frozen_string_literal: true

class Optional
  attr_reader :value

  def initialize(value)
    @value = value
  end

  def then(&block)
    return enum_for __method__ unless block_given?
    return self.class.none if @value.nil?

    @value.public_send __method__, &block
  end

  class << self
    def none
      new nil
    end

    alias some new
  end
end

a = Optional.some(42)
b = Optional.some(a)
c = Optional.some(b)
d = Optional.some(c)
d.then.first
#=> 42

f = Optional.none
g = Optional.some(f)
g.then.first
#=> nil

Pickle = Struct.new :jar
Jar = Struct.new :label
Label = Struct.new :words

label = Optional.some Label.new 'Bubbies'
jar = Optional.some Jar.new label
pickle = Optional.some Pickle.new jar
pickle.then(&:jar).then(&:label).then(&:words)
#=> "Bubbies"

no_jar = Optional.none
another_pickle = Optional.some Pickle.new no_jar
another_pickle.then(&:jar).then(&:label).then(&:words)
#=> #<Optional:... @value=nil>