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, 22 insertions, 0 deletions

diff --git a/activesupport/test/core_ext/module_test.rb b/activesupport/test/core_ext/module_test.rb
index 0ed66f8c37..ed9cf897a4 100644
--- a/activesupport/test/core_ext/module_test.rb
+++ b/activesupport/test/core_ext/module_test.rb
@@ -83,6 +83,20 @@ Product = Struct.new(:name) do
   end
 end
 
+DecoratedTester = Struct.new(:client) do
+  delegate_missing_to :client
+end
+
+class DecoratedReserved
+  delegate_missing_to :case
+
+  attr_reader :case
+
+  def initialize(kase)
+    @case = kase
+  end
+end
+
 class Block
   def hello?
     true
@@ -316,6 +330,14 @@ class ModuleTest < ActiveSupport::TestCase
     assert has_block.hello?
   end
 
+  def test_delegate_to_missing_with_method
+    assert_equal "David", DecoratedTester.new(@david).name
+  end
+
+  def test_delegate_to_missing_with_reserved_methods
+    assert_equal "David", DecoratedReserved.new(@david).name
+  end
+
   def test_parent
     assert_equal Yz::Zy, Yz::Zy::Cd.parent
     assert_equal Yz, Yz::Zy.parent