Added delegation support to Module that allows multiple delegations at once (unlike Forwardable in the stdlib) [DHH]

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@3535 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

activesupport/CHANGELOG

@@ -1,5 +1,16 @@
 *SVN*
 
+* Added delegation support to Module that allows multiple delegations at once (unlike Forwardable in the stdlib) [DHH]. Example:
+
+    class Account < ActiveRecord::Base
+      has_one :subscription
+      delegate :free?, :paying?, :to => :subscription
+      delegate :overdue?, :to => "subscription.last_payment"
+    end
+    
+    account.free?    # => account.subscription.free?
+    account.overdue? # => account.subscription.last_payment.overdue?
+
 * Fix Reloadable to handle the case where a class that has been 'removed' has not yet been garbage collected. [Nicholas Seckar]
 
 * Don't allow Reloadable to be included into Modules.

activesupport/lib/active_support/core_ext/module.rb

@@ -1,2 +1,3 @@
 require File.dirname(__FILE__) + '/module/inclusion'
-require File.dirname(__FILE__) + '/module/attribute_accessors'
+require File.dirname(__FILE__) + '/module/attribute_accessors'
+require File.dirname(__FILE__) + '/module/delegation'

activesupport/lib/active_support/core_ext/module/delegation.rb

@@ -0,0 +1,16 @@
+class Module
+  def delegate(*methods)
+    options = methods.pop
+    unless options.is_a?(Hash) && to = options[:to]
+      raise ArgumentError, "Delegation needs a target. Supply an options hash with a :to key"
+    end
+
+    methods.each do |method|
+      module_eval(<<-EOS, "(__DELEGATION__)", 1)
+        def #{method}(*args, &block)
+          #{to}.__send__(#{method.inspect}, *args, &block)
+        end
+      EOS
+    end
+  end
+end

activesupport/test/core_ext/module_test.rb

@@ -26,6 +26,34 @@ end
 class De
 end
 
+Somewhere = Struct.new(:street, :city)
+
+Someone   = Struct.new(:name, :place) do
+  delegate :street, :city, :to => :place
+  delegate :state, :to => :@place
+  delegate :upcase, :to => "place.city"
+end
+
+class Name
+  delegate :upcase, :to => :@full_name
+
+  def initialize(first, last)
+    @full_name = "#{first} #{last}"
+  end
+end
+
+$nowhere = <<-EOF
+class Name
+  delegate :nowhere
+end
+EOF
+
+$noplace = <<-EOF
+class Name
+  delegate :noplace, :tos => :hollywood
+end
+EOF
+
 class ModuleTest < Test::Unit::TestCase
   def test_included_in_classes
     assert One.included_in_classes.include?(Ab)
@@ -34,4 +62,24 @@ class ModuleTest < Test::Unit::TestCase
     assert !One.included_in_classes.include?(De)
   end
 
+  def test_delegation_to_methods
+    david = Someone.new("David", Somewhere.new("Paulina", "Chicago"))
+    assert_equal "Paulina", david.street
+    assert_equal "Chicago", david.city
+  end
+  
+  def test_delegation_down_hierarchy
+    david = Someone.new("David", Somewhere.new("Paulina", "Chicago"))
+    assert_equal "CHICAGO", david.upcase
+  end
+  
+  def test_delegation_to_instance_variable
+    david = Name.new("David", "Hansson")
+    assert_equal "DAVID HANSSON", david.upcase
+  end
+  
+  def test_missing_delegation_target
+    assert_raises(ArgumentError) { eval($nowhere) }
+    assert_raises(ArgumentError) { eval($noplace) }
+  end
 end