A writer addition for Rails' delagate feature.

delegate_writer.patch

diff --git a/.gitignore b/.gitignore
index 2dfdf96..79d884c 100644
--- a/.gitignore
+++ b/.gitignore
@@ -19,3 +19,5 @@ railties/test/initializer/root/log
 railties/doc
 railties/guides/output
 railties/tmp
+.DS_Store
+nbproject
diff --git a/activesupport/lib/active_support/core_ext/module/delegation.rb b/activesupport/lib/active_support/core_ext/module/delegation.rb
index 3a7652f..9ccb2b6 100644
--- a/activesupport/lib/active_support/core_ext/module/delegation.rb
+++ b/activesupport/lib/active_support/core_ext/module/delegation.rb
@@ -109,11 +109,12 @@ class Module
       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
 
-    if options[:prefix] == true && options[:to].to_s =~ /^[^a-z_]/
-      raise ArgumentError, "Can only automatically set the delegation prefix when delegating to a method."
+    if (options[:prefix] == true || options[:writer]) && options[:to].to_s =~ /^[^a-z_]/
+      raise ArgumentError, "Can only automatically set the delegation prefix or make a writer method when delegating to a method."
     end
 
     prefix = options[:prefix] && "#{options[:prefix] == true ? to : options[:prefix]}_" || ''
+    writer = !!options[:writer]
 
     file, line = caller.first.split(':', 2)
     line = line.to_i
@@ -141,6 +142,24 @@ class Module
           end                                               #   end
         end                                                 # end
       EOS
+      
+      if writer
+        module_eval(<<-EOS, file, line - 5)
+          if instance_methods(false).map(&:to_s).include?("#{prefix}#{method}=")
+            remove_possible_method("#{prefix}#{method}=")
+          end
+
+          def #{prefix}#{method}=(*args, &block)              # def customer_name=(*args, &block)
+            #{to}.__send__(#{method.inspect}=, *args, &block) #   client.__send__(:name=, *args, &block)
+          rescue NoMethodError                                # rescue NoMethodError
+            if #{to}.nil?                                     #   if client.nil?
+              #{on_nil}                                       #     return # depends on :allow_nil
+            else                                              #   else
+              raise                                           #     raise
+            end                                               #   end
+          end                                                 # end
+        EOS
+      end
     end
   end
 end
diff --git a/activesupport/test/core_ext/module_test.rb b/activesupport/test/core_ext/module_test.rb
index 75404ec..0841711 100644
--- a/activesupport/test/core_ext/module_test.rb
+++ b/activesupport/test/core_ext/module_test.rb
@@ -42,6 +42,10 @@ Invoice   = Struct.new(:client) do
   delegate :street, :city, :name, :to => :client, :prefix => :customer
 end
 
+Bill      = Struct.new(:client) do
+  delegate :name, :to => :client, :prefix => true, :writer => true
+end
+
 Project   = Struct.new(:description, :person) do
   delegate :name, :to => :person, :allow_nil => true
   delegate :to_f, :to => :description, :allow_nil => true
@@ -82,6 +86,12 @@ class ModuleTest < Test::Unit::TestCase
     assert_equal "DAVID HANSSON", david.upcase
   end
 
+  def test_delegation_to_methods_with_writer
+    bill = Bill.new(@david)
+    bill.client_name = "Nathan"
+    assert_equal "Nathan", bill.client_name
+  end
+
   def test_missing_delegation_target
     assert_raise(ArgumentError) do
       Name.send :delegate, :nowhere