A type of module combining distinct from include/extend

combine.rb

module HappehTheory
  module SingleCell
    def gelatin
      trait
    end
    
    private
    
    def trait(*args)
      "a flagellum"
    end
  end
  
  
  module Fish
    def pyramid
      trait
    end
    
    private
    
    def trait(*args)
      "a spine"
    end
  end
  
  
  module Amphibian
    def lick
      trait
    end
    
    private
    
    def trait(*args)
      "a tongue"
    end
  end
  
  
  module Reptile
    def punch
      trait
    end
    
    private
    
    def trait(*args)
      "an arm"
    end
  end
  
  
  module Insect
    def peer
      trait
    end
    
    private
    
    def trait(*args)
      "an eyeball"
    end
  end
  
  
  module Bird
    def dance
      trait
    end
    
    private
    
    def trait(*args)
      "a foot"
    end
  end
  
  
  module Mammal
    def reproduce
      trait
    end
    
    private
    
    def trait(*args)
      "a live birth"
    end
  end
  
  
  class Human
    
    def combine mod
      singleton_class = (class << self; self; end)
      @combined_module_context ||= {}
      
      # Wrap public methods to set the context variable
      mod.instance_methods.each do |sym|
        singleton_class.send :define_method, sym do |*args, &block|
          saved = @combined_module_context[Thread.current]
          @combined_module_context[Thread.current] = mod
          mod.instance_method(sym).bind(self).call(*args, &block)
            .tap { @combined_module_context[Thread.current] = saved }
        end
      end
      
      # Wrap private methods to call the right method based on context
      mod.private_instance_methods.each do |sym|
        singleton_class.send :define_method, sym do |*args, &block|
          this_mod = @combined_module_context[Thread.current]
          raise NoMethodError, "private method ##{sym}" unless this_mod
          this_mod.instance_method(sym).bind(self).call(*args, &block)
        end
      end
    end
    
    def initialize *args
      yield self
    end
  end
  
end


include HappehTheory

h = Human.new do |d|
  d.combine SingleCell
  d.combine Fish
  d.combine Amphibian
  d.combine Reptile
  d.combine Insect
  d.combine Bird
  d.combine Mammal
end

require 'pry'
binding.pry