Document the changes to delegate in the guides

1 files changed, 20 insertions, 0 deletions

diff --git a/guides/source/active_support_core_extensions.textile b/guides/source/active_support_core_extensions.textile
index 5d0a3f82e8..181dac72cf 100644
--- a/guides/source/active_support_core_extensions.textile
+++ b/guides/source/active_support_core_extensions.textile
@@ -883,6 +883,26 @@ delegate :size, :to => :attachment, :prefix => :avatar
 
 In the previous example the macro generates +avatar_size+ rather than +size+.
 
+WARNING: You can only delegate to public methods on the target object. Trying to delegate to a private or protected method will raise a +NoMethodError+ when the delegate is called.
+
+If you need to delegate to a private or protected method, you will need to implement the delegation method yourself. It's usually rather simple to do using +__send__+:
+
+<ruby>
+class Wrapper
+  def initialize
+    # Target#zizzle is a private method.
+    @target = Target.new
+  end
+
+  def zizzle(*args, &block)
+    # __send__ circumvents the private/protected mechanism.
+    @target.__send__(:zizzle, *args, &block)
+  end
+end
+</ruby>
+
+Since +__send__+ can be used to call private and protected methods, this will not raise a +NoMethodError+.
+
 NOTE: Defined in +active_support/core_ext/module/delegation.rb+
 
 h4. Redefining Methods