From 5362d6ccbb12d5cd92597de5248cd62dab46a76d Mon Sep 17 00:00:00 2001
From: Sergio Gil <sgilperez@gmail.com>
Date: Sat, 27 Sep 2008 21:33:11 +0200
Subject: [PATCH] Added :allow_nil option for delegate

---
 .../active_support/core_ext/module/delegation.rb   |   28 +++++++++++++++++++-
 activesupport/test/core_ext/module_test.rb         |   21 ++++++++++++++-
 2 files changed, 47 insertions(+), 2 deletions(-)

diff --git a/activesupport/lib/active_support/core_ext/module/delegation.rb b/activesupport/lib/active_support/core_ext/module/delegation.rb
index e0b5f3e..8491bad 100644
--- a/activesupport/lib/active_support/core_ext/module/delegation.rb
+++ b/activesupport/lib/active_support/core_ext/module/delegation.rb
@@ -47,16 +47,42 @@ class Module
   #   Foo.new.min # => 4
   #   Foo.new.max # => 11
   #
+  # If the object in which you delegate can be nil, you may want to use the
+  # :allow_nil option. In that case, it returns nil instead of raising a
+  # NoMethodError exception:
+  #
+  #  class Foo
+  #    attr_accessor :bar
+  #    def initialize(bar = nil)
+  #      @bar = bar
+  #    end
+  #    delegate :zoo, :to => :bar
+  #  end
+  #  
+  #  Foo.new.zoo   # raises NoMethodError exception (you called nil.zoo)
+  #  
+  #  class Foo
+  #    attr_accessor :bar
+  #    def initialize(bar = nil)
+  #      @bar = bar
+  #    end
+  #    delegate :zoo, :to => :bar, :allow_nil => true
+  #  end
+  #  
+  #  Foo.new.zoo   # returns nil
+  #
   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 as the last argument (e.g. delegate :hello, :to => :greeter)."
     end
+    
+    allow_nil = options[:allow_nil] && "#{to} && "
 
     methods.each do |method|
       module_eval(<<-EOS, "(__DELEGATION__)", 1)
         def #{method}(*args, &block)
-          #{to}.__send__(#{method.inspect}, *args, &block)
+          #{allow_nil}#{to}.__send__(#{method.inspect}, *args, &block)
         end
       EOS
     end
diff --git a/activesupport/test/core_ext/module_test.rb b/activesupport/test/core_ext/module_test.rb
index ecdea38..e083379 100644
--- a/activesupport/test/core_ext/module_test.rb
+++ b/activesupport/test/core_ext/module_test.rb
@@ -36,6 +36,10 @@ Someone   = Struct.new(:name, :place) do
   delegate :upcase, :to => "place.city"
 end
 
+Project   = Struct.new(:description, :person) do
+  delegate :name, :to => :person, :allow_nil => true
+end
+
 class Name
   delegate :upcase, :to => :@full_name
 
@@ -84,7 +88,22 @@ class ModuleTest < Test::Unit::TestCase
     assert_raises(ArgumentError) { eval($nowhere) }
     assert_raises(ArgumentError) { eval($noplace) }
   end
-
+  
+  def test_delegation_with_allow_nil
+    rails = Project.new("Rails", Someone.new("David"))
+    assert_equal rails.name, "David"
+  end
+  
+  def test_delegation_with_allow_nil_and_nil_value
+    rails = Project.new("Rails")
+    assert_nil rails.name
+  end
+  
+  def test_delegation_without_allow_nil_and_nil_value
+    david = Someone.new("David")
+    assert_raises(NoMethodError) { david.street }
+  end
+  
   def test_parent
     assert_equal Yz::Zy, Yz::Zy::Cd.parent
     assert_equal Yz, Yz::Zy.parent
-- 
1.5.3.7