Sample Code

README

@@ -0,0 +1 @@
+Sample code for the RubySource article [Making Ruby Quack—Why We Love Duck Typing](http://rubysource.com)

example.rb

@@ -0,0 +1,35 @@
+class ShippingManifest
+  attr_accessor :mass, :package_count
+
+  def initialize(mass, package_count)
+    @mass          = mass
+    @package_count = package_count
+  end
+
+  def +(other)
+    self.dup.tap do |neu|
+      neu.mass          = self.mass + other.mass
+      neu.package_count = self.package_count + other.package_count
+    end
+  end
+end
+
+
+# Addition:
+shipping_manifest_one = ShippingManifest.new(5, 10)
+shipping_manifest_two = ShippingManifest.new(1, 1)
+shipping_manifest_sum = shipping_manifest_one + shipping_manifest_two
+
+shipping_manifest_sum.package_count # => 11
+shipping_manifest_sum.mass          # => 6
+
+puts "shipping_manifest_sum: #{shipping_manifest_sum.inspect}"
+
+# Injection:
+manifests = [
+  ShippingManifest.new(5, 10),
+  ShippingManifest.new(1, 1),
+  ShippingManifest.new(35, 50),  
+]
+
+manifests.inject { |sum, m| sum + m } # => #<ShippingManifest:0x100164c38 @package_count=61, @mass=41>