1 files changed, 77 insertions, 16 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..f5f4ba61b7 100644
--- a/activesupport/lib/active_support/core_ext/module/delegation.rb
+++ b/activesupport/lib/active_support/core_ext/module/delegation.rb
@@ -1,4 +1,5 @@
-require 'set'
+require "set"
+require "active_support/core_ext/regexp"
 
 class Module
   # Error generated by +delegate+ when a method is called on +nil+ and +allow_nil+
@@ -148,28 +149,24 @@ 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]
-      raise ArgumentError, 'Delegation needs a target. Supply an options hash with a :to key as the last argument (e.g. delegate :hello, to: :greeter).'
+  def delegate(*methods, to: nil, prefix: nil, allow_nil: nil)
+    unless 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
 
-    prefix, allow_nil = options.values_at(:prefix, :allow_nil)
-
-    if prefix == true && to =~ /^[^a-z_]/
-      raise ArgumentError, 'Can only automatically set the delegation prefix when delegating to a method.'
+    if prefix == true && /^[^a-z_]/.match?(to)
+      raise ArgumentError, "Can only automatically set the delegation prefix when delegating to a method."
     end
 
     method_prefix = \
       if prefix
         "#{prefix == true ? to : prefix}_"
       else
-        ''
+        ""
       end
 
-    file, line = caller(1, 1).first.split(':'.freeze, 2)
-    line = line.to_i
+    location = caller_locations(1, 1).first
+    file, line = location.path, location.lineno
 
     to = to.to_s
     to = "self.#{to}" if DELEGATION_RESERVED_METHOD_NAMES.include?(to)
@@ -177,7 +174,7 @@ class Module
     methods.each do |method|
       # Attribute writer methods only accept one argument. Makes sure []=
       # methods still accept two arguments.
-      definition = (method =~ /[^\]]=$/) ? 'arg' : '*args, &block'
+      definition = /[^\]]=$/.match?(method) ? "arg" : "*args, &block"
 
       # The following generated method calls the target exactly once, storing
       # the returned value in a dummy variable.
@@ -194,7 +191,7 @@ class Module
           "  _.#{method}(#{definition})",
           "end",
         "end"
-        ].join ';'
+        ].join ";"
       else
         exception = %(raise DelegationError, "#{self}##{method_prefix}#{method} delegated to #{to}.#{method}, but #{to} is nil: \#{self.inspect}")
 
@@ -209,10 +206,74 @@ class Module
           "    raise",
           "  end",
           "end"
-        ].join ';'
+        ].join ";"
       end
 
       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 within 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)
+        if #{target}.respond_to?(method)
+          #{target}.public_send(method, *args, &block)
+        else
+          super
+        end
+      end
+    RUBY
+  end
 end