invisible_proxy.rb

class FlatArray
  instance_methods.each do |m|
    undef_method(m) unless m =~ /(^__|^nil\?|^send$|^object_id$)/
  end

  def initialize(array)
    @target = array
  end

  def respond_to?(symbol, include_priv=false)
    @target.respond_to?(symbol, include_priv)
  end

  def <<(object)
    if object.is_a? Array
      @target += object
    else
      @target << object
    end
  end

  private

  def method_missing(method, *args, &block)
    @target.send(method, *args, &block)
  end
end

a = [1, 2, 3, 4]
puts "a.class = #{a.class}"
puts "a = #{a.inspect}"

a << [5, 6, 7]
puts "a = #{a.inspect}"

b = FlatArray.new([1, 2, 3, 4])
puts "b.class = #{b.class}"
puts "b = #{b.inspect}"

b << [5, 6, 7]
puts "b = #{b.inspect}"