Refactoring #method_missing to define a previously missing method in the Decorator when calling it for the first time.

lib/draper/base.rb

@@ -157,7 +157,10 @@ module Draper
     def method_missing(method, *args, &block)
       if allow?(method)
         begin
-          model.send(method, *args, &block)
+          self.class.send :define_method, method do |*args, &block|
+            model.send(method, *args, &block)
+          end
+          self.send(method, *args, &block)
         rescue NoMethodError
           super
         end

performance/active_record.rb

@@ -0,0 +1,4 @@
+module ActiveRecord
+  class Base
+  end
+end

performance/bechmark.rb

@@ -0,0 +1,55 @@
+require 'rubygems'
+ENV['BUNDLE_GEMFILE'] ||= File.expand_path('../../Gemfile', __FILE__)
+require 'bundler/setup' if File.exists?(ENV['BUNDLE_GEMFILE'])
+Bundler.require(:default) if defined?(Bundler)
+
+require "benchmark"
+require "draper"
+require "./performance/models"
+require "./performance/decorators"
+
+Benchmark.bm do |bm|
+  puts "\n[ Exclusivelly using #method_missing for model delegation ]"
+  [ 1_000, 10_000, 100_000 ].each do |i|
+    puts "\n[ #{i} ]"
+    bm.report("#new                 ") do
+      i.times do |n|
+        ProductDecorator.decorate(Product.new)
+      end
+    end
+    
+    bm.report("#hello_world         ") do
+      i.times do |n|
+        ProductDecorator.decorate(Product.new).hello_world
+      end
+    end
+    
+    bm.report("#sample_class_method ") do
+      i.times do |n|
+        ProductDecorator.decorate(Product.new).class.sample_class_method
+      end
+    end
+  end
+  
+  puts "\n[ Defining methods on method_missing first hit ]"
+  [ 1_000, 10_000, 100_000 ].each do |i|
+    puts "\n[ #{i} ]"
+    bm.report("#new                 ") do
+      i.times do |n|
+        FastProductDecorator.decorate(FastProduct.new)
+      end
+    end
+    
+    bm.report("#hello_world         ") do
+      i.times do |n|
+        FastProductDecorator.decorate(FastProduct.new).hello_world
+      end
+    end
+    
+    bm.report("#sample_class_method ") do
+      i.times do |n|
+        FastProductDecorator.decorate(FastProduct.new).class.sample_class_method
+      end
+    end
+  end
+end

performance/decorators.rb

@@ -0,0 +1,47 @@
+require "./performance/models"
+class ProductDecorator < Draper::Base
+  decorates :product
+  
+  def awesome_title
+    "Awesome Title"
+  end
+  
+  # Original #method_missing
+  def method_missing(method, *args, &block)
+    if allow?(method)
+      begin
+        model.send(method, *args, &block)
+      rescue NoMethodError
+        super
+      end
+    else
+      super
+    end
+  end
+
+end
+
+class FastProductDecorator < Draper::Base
+  decorates :product
+  
+  def awesome_title
+    "Awesome Title"
+  end
+  
+  # Modified #method_missing
+  def method_missing(method, *args, &block)
+    if allow?(method)
+      begin
+        self.class.send :define_method, method do |*args, &block|
+          model.send(method, *args, &block)
+        end
+        self.send(method, *args, &block)
+      rescue NoMethodError
+        super
+      end
+    else
+      super
+    end
+  end
+
+end

performance/models.rb

@@ -0,0 +1,20 @@
+require "./performance/active_record"
+class Product < ActiveRecord::Base
+  def self.sample_class_method
+    "sample class method"
+  end
+  
+  def hello_world
+    "Hello, World"
+  end
+end
+
+class FastProduct < ActiveRecord::Base
+  def self.sample_class_method
+    "sample class method"
+  end
+  
+  def hello_world
+    "Hello, World"
+  end
+end

spec/draper/base_spec.rb

@@ -382,4 +382,21 @@ describe Draper::Base do
       subject.kind_of?(source.class).should == true
     end
   end
+  
+  describe "#method_missing" do
+    context "when #hello_world is called for the first time" do
+      it "hits method missing" do
+        subject.should_receive(:method_missing)
+        subject.hello_world
+      end
+    end
+    
+    context "when #hello_world is called again" do
+      before { subject.hello_world }
+      it "proxies method directly after first hit" do
+        subject.should_not_receive(:method_missing)
+        subject.hello_world
+      end
+    end
+  end
 end