Add :allow_nil option to delegate [#1127 state:resolved]

Signed-off-by: Pratik Naik <pratiknaik@gmail.com>

activesupport/CHANGELOG

@@ -1,5 +1,7 @@
 *2.3.0 [Edge]*
 
+* Add :allow_nil option to delegate. #1127 [Sergio Gil]
+
 * Add Benchmark.ms convenience method to benchmark realtime in milliseconds.  [Jeremy Kemper]
 
 * Updated included memcache-client to the 1.5.0.5 version which includes fixes from fiveruns and 37signals to deal with failover and timeouts #1535 [Joshua Sierles]

activesupport/lib/active_support/core_ext/module/delegation.rb

@@ -72,6 +72,30 @@ class Module
   #   invoice.customer_name    # => "John Doe"
   #   invoice.customer_address # => "Vimmersvej 13"
   #
+  # If the object to which you delegate can be nil, you may want to use the
+  # :allow_nil option. In that case, it returns nil instead of raising a
+  # NoMethodError exception:
+  #
+  #  class Foo
+  #    attr_accessor :bar
+  #    def initialize(bar = nil)
+  #      @bar = bar
+  #    end
+  #    delegate :zoo, :to => :bar
+  #  end
+  #
+  #  Foo.new.zoo   # raises NoMethodError exception (you called nil.zoo)
+  #
+  #  class Foo
+  #    attr_accessor :bar
+  #    def initialize(bar = nil)
+  #      @bar = bar
+  #    end
+  #    delegate :zoo, :to => :bar, :allow_nil => true
+  #  end
+  #
+  #  Foo.new.zoo   # returns nil
+  #
   def delegate(*methods)
     options = methods.pop
     unless options.is_a?(Hash) && to = options[:to]
@@ -84,10 +108,12 @@ def delegate(*methods)
 
     prefix = options[:prefix] && "#{options[:prefix] == true ? to : options[:prefix]}_"
 
+    allow_nil = options[:allow_nil] && "#{to} && "
+
     methods.each do |method|
       module_eval(<<-EOS, "(__DELEGATION__)", 1)
         def #{prefix}#{method}(*args, &block)
-          #{to}.__send__(#{method.inspect}, *args, &block)
+          #{allow_nil}#{to}.__send__(#{method.inspect}, *args, &block)
         end
       EOS
     end

activesupport/test/core_ext/module_test.rb

@@ -41,6 +41,10 @@ class De
   delegate :street, :city, :name, :to => :client, :prefix => :customer
 end
 
+Project   = Struct.new(:description, :person) do
+  delegate :name, :to => :person, :allow_nil => true
+end
+
 class Name
   delegate :upcase, :to => :@full_name
 
@@ -117,6 +121,29 @@ def initialize(client)
     end
   end
 
+  def test_delegation_with_allow_nil
+    rails = Project.new("Rails", Someone.new("David"))
+    assert_equal rails.name, "David"
+  end
+
+  def test_delegation_with_allow_nil_and_nil_value
+    rails = Project.new("Rails")
+    assert_nil rails.name
+  end
+
+  def test_delegation_with_allow_nil_and_nil_value_and_prefix
+    Project.class_eval do
+      delegate :name, :to => :person, :allow_nil => true, :prefix => true
+    end
+    rails = Project.new("Rails")
+    assert_nil rails.person_name
+  end
+
+  def test_delegation_without_allow_nil_and_nil_value
+    david = Someone.new("David")
+    assert_raises(NoMethodError) { david.street }
+  end
+
   def test_parent
     assert_equal Yz::Zy, Yz::Zy::Cd.parent
     assert_equal Yz, Yz::Zy.parent