3 files changed, 74 insertions, 0 deletions
diff --git a/activesupport/CHANGELOG b/activesupport/CHANGELOG
index 373236ce9a..8e7e2d188b 100644
--- a/activesupport/CHANGELOG
+++ b/activesupport/CHANGELOG
@@ -1,5 +1,7 @@
 *Rails 3.1.0 (unreleased)*
 
+* Add Object#in? to test if an object is included in another object, and Object#either? to test if an object is included in a list of objects which will be passed as arguments. [Prem Sichanugrist, Brian Morearty, John Reitano]
+
 * LocalCache strategy is now a real middleware class, not an anonymous class
 posing for pictures.
 
diff --git a/activesupport/lib/active_support/core_ext/object/inclusion.rb b/activesupport/lib/active_support/core_ext/object/inclusion.rb
new file mode 100644
index 0000000000..79e9fd6c88
--- /dev/null
+++ b/activesupport/lib/active_support/core_ext/object/inclusion.rb
@@ -0,0 +1,20 @@
+class Object
+  # Returns true if this object is included in the argument. Argument must be
+  # any object which respond to +#include?+. Usage:
+  #
+  #   characters = ["Konata", "Kagami", "Tsukasa"]
+  #   "Konata".in?(characters) # => true
+  #
+  def in?(another_object)
+    another_object.include?(self)
+  end
+
+  # Returns true if this object is included in the argument list. Usage:
+  #
+  #   username = "sikachu"
+  #   username.either?("josevalim", "dhh", "wycats") # => false
+  #
+  def either?(*objects)
+    objects.include?(self)
+  end
+end
diff --git a/activesupport/test/core_ext/object/inclusion_test.rb b/activesupport/test/core_ext/object/inclusion_test.rb
new file mode 100644
index 0000000000..b4207c20ea
--- /dev/null
+++ b/activesupport/test/core_ext/object/inclusion_test.rb
@@ -0,0 +1,52 @@
+require 'abstract_unit'
+require 'active_support/core_ext/object/inclusion'
+
+class InTest < Test::Unit::TestCase
+  def test_in_array
+    assert 1.in?([1,2])
+    assert !3.in?([1,2])
+  end
+
+  def test_in_hash
+    h = { "a" => 100, "b" => 200 }
+    assert "a".in?(h)
+    assert !"z".in?(h)
+  end
+
+  def test_in_string
+    assert "lo".in?("hello")
+    assert !"ol".in?("hello")
+    assert ?h.in?("hello")
+  end
+
+  def test_in_range
+    assert 25.in?(1..50)
+    assert !75.in?(1..50)
+  end
+
+  def test_in_set
+    s = Set.new([1,2])
+    assert 1.in?(s)
+    assert !3.in?(s)
+  end
+
+  def test_either
+    assert 1.either?(1,2,3)
+    assert !5.either?(1,2,3)
+    assert [1,2,3].either?([1,2,3], 2, [3,4,5])
+  end
+
+  module A
+  end
+  class B
+    include A
+  end
+  class C < B
+  end
+
+  def test_in_module
+    assert A.in?(B)
+    assert A.in?(C)
+    assert !A.in?(A)
+  end
+end