Spiking a slimline no work allowed approach to constructors in Ruby.

slim_const_spike.rb

require 'rspec'

module Hardline
  def self.extended(base)
    base.define_singleton_method(:construct_with) do |*args|
      base.define_singleton_method(:new) do |*init_args|
        combined_args = args.zip(init_args)
        me = self.allocate
        me.tap do |obj|
          combined_args.map do |(n, v)|
            obj.instance_variable_set("@#{n}", v)
          end
        end
      end
    end
  end
end

class Foo
  extend Hardline

  construct_with(:var1, :var2)
end

describe Foo do
  subject{ Foo.new("hello", "kitty") }

  it "should create a new object" do
    subject.should be_a(Foo)
  end

  it "should assign instance vars as specified in constructor" do
    subject.instance_variable_get("@var1").should eq "hello"
    subject.instance_variable_get("@var2").should eq "kitty"
  end
end