initial implementation + specs

cls.rb

@@ -0,0 +1,25 @@
+module Cls
+  def self.included(base)
+    base.send :extend, ClassMethods
+  end
+
+  module ClassMethods
+    def takes(*args)
+      define_initialize(args)
+    end
+
+    def define_initialize(args)
+      assignments = args.map { |a| "@#{a} = #{a}" }.join("\n")
+      self.class_eval %{
+        def initialize(#{args.join(", ")})
+          #{assignments}
+        end
+      }
+    end
+
+    def let(name, &block)
+      define_method(name, &block)
+    end
+  end
+end
+

spec/cls_spec.rb

@@ -0,0 +1,61 @@
+require "./cls"
+
+class NamePresenter
+  include Cls
+  attr_reader :name
+  takes(:name)
+  let(:yelled_name) { @name.upcase }
+  let(:name_with_argument) { |other| }
+  let(:increment) { @value ||= 0; @value += 1 }
+end
+
+describe Cls do
+  describe "initializers" do
+    it "takes initializer arguments" do
+      NamePresenter.new("Bob").name.should == "Bob"
+    end
+
+    it "errors when there are too many initializer arguments" do
+      expect do
+        NamePresenter.new("Bob", "Smith")
+      end.to raise_error(ArgumentError)
+    end
+
+    it "errors when there are too few initializer arguments" do
+      expect do
+        NamePresenter.new
+      end.to raise_error(ArgumentError)
+    end
+  end
+
+  describe "let methods" do
+    let(:presenter) { NamePresenter.new("Bob") }
+
+    it "defines methods" do
+      presenter.yelled_name.should == "BOB"
+    end
+
+    it "does not cache method return values" do
+      presenter.increment.should_not == presenter.increment
+    end
+
+    it "errors when there are too many method arguments" do
+      expect do
+        presenter.yelled_name("extra argument")
+      end.to raise_error(ArgumentError)
+    end
+
+    it "errors when there are too few method arguments" do
+      expect do
+        presenter.name_with_argument
+      end.to raise_error(ArgumentError)
+    end
+  end
+
+  it "doesn't pollute other classes" do
+    expect do
+      Class.new { takes :name }
+    end.to raise_error(NameError)
+  end
+end
+