Introduce Module#delegate_missing_to

When building decorators, a common pattern may emerge:

    class Partition
      def initialize(first_event)
        @events = [ first_event ]
      end

      def people
        if @events.first.detail.people.any?
          @events.collect { |e| Array(e.detail.people) }.flatten.uniq
        else
          @events.collect(&:creator).uniq
        end
      end

      private
        def respond_to_missing?(name, include_private = false)
          @events.respond_to?(name, include_private)
        end

        def method_missing(method, *args, &block)
          @events.send(method, *args, &block)
        end
    end

With `Module#delegate_missing_to`, the above is condensed to:

    class Partition
      delegate_missing_to :@events

      def initialize(first_event)
        @events = [ first_event ]
      end

      def people
        if @events.first.detail.people.any?
          @events.collect { |e| Array(e.detail.people) }.flatten.uniq
        else
          @events.collect(&:creator).uniq
        end
      end
    end

David suggested it in #23824.

1 files changed, 60 insertions, 1 deletions

diff --git a/activesupport/lib/active_support/core_ext/module/delegation.rb b/activesupport/lib/active_support/core_ext/module/delegation.rb
index 0d46248582..a97a4add93 100644
--- a/activesupport/lib/active_support/core_ext/module/delegation.rb
+++ b/activesupport/lib/active_support/core_ext/module/delegation.rb
@@ -148,7 +148,6 @@ class Module
   #   Foo.new("Bar").name # raises NoMethodError: undefined method `name'
   #
   # The target method must be public, otherwise it will raise +NoMethodError+.
-  #
   def delegate(*methods)
     options = methods.pop
     unless options.is_a?(Hash) && to = options[:to]
@@ -215,4 +214,64 @@ class Module
       module_eval(method_def, file, line)
     end
   end
+
+  # When building decorators, a common pattern may emerge:
+  #
+  #   class Partition
+  #     def initialize(first_event)
+  #       @events = [ first_event ]
+  #     end
+  #
+  #     def people
+  #       if @events.first.detail.people.any?
+  #         @events.collect { |e| Array(e.detail.people) }.flatten.uniq
+  #       else
+  #         @events.collect(&:creator).uniq
+  #       end
+  #     end
+  #
+  #     private
+  #       def respond_to_missing?(name, include_private = false)
+  #         @events.respond_to?(name, include_private)
+  #       end
+  #
+  #       def method_missing(method, *args, &block)
+  #         @events.send(method, *args, &block)
+  #       end
+  #   end
+  #
+  # With `Module#delegate_missing_to`, the above is condensed to:
+  #
+  #   class Partition
+  #     delegate_missing_to :@events
+  #
+  #     def initialize(first_event)
+  #       @events = [ first_event ]
+  #     end
+  #
+  #     def people
+  #       if @events.first.detail.people.any?
+  #         @events.collect { |e| Array(e.detail.people) }.flatten.uniq
+  #       else
+  #         @events.collect(&:creator).uniq
+  #       end
+  #     end
+  #   end
+  #
+  # The target can be anything callable withing the object. E.g. instance
+  # variables, methods, constants ant the likes.
+  def delegate_missing_to(target)
+    target = target.to_s
+    target = "self.#{target}" if DELEGATION_RESERVED_METHOD_NAMES.include?(target)
+
+    module_eval <<-RUBY, __FILE__, __LINE__ + 1
+      def respond_to_missing?(name, include_private = false)
+        #{target}.respond_to?(name, include_private)
+      end
+
+      def method_missing(method, *args, &block)
+        #{target}.send(method, *args, &block)
+      end
+    RUBY
+  end
 end