2 files changed, 74 insertions, 0 deletions
diff --git a/activesupport/lib/active_support/weak_hash.rb b/activesupport/lib/active_support/weak_hash.rb
new file mode 100644
index 0000000000..d6096e606e
--- /dev/null
+++ b/activesupport/lib/active_support/weak_hash.rb
@@ -0,0 +1,41 @@
+module ActiveSupport
+  if defined?(RUBY_ENGINE) && RUBY_ENGINE == 'jruby'
+    WeakHash = ::Weakling::WeakHash
+  else
+    class WeakHash
+      def initialize(cache = Hash.new)
+        @cache = cache
+        @key_map = {}
+        @rev_cache = Hash.new{|h,k| h[k] = {}}
+        @reclaim_value = lambda do |value_id|
+          if value = @rev_cache.delete(value_id)
+            value.each_key{|key| @cache.delete key}
+          end
+        end
+      end
+
+      def [](key)
+        value_id = @cache[key]
+        value_id && ObjectSpace._id2ref(value_id)
+      rescue RangeError
+        nil
+      end
+
+      def []=(key, value)
+        @rev_cache[value.object_id][key] = true
+        @cache[key] = value.object_id
+        @key_map[key.object_id] = key
+
+        ObjectSpace.define_finalizer(value, @reclaim_value)
+      end
+
+      def clear
+        @cache.clear
+      end
+
+      def delete(key)
+        @cache.delete(key)
+      end
+    end
+  end
+end
diff --git a/activesupport/test/weak_hash_test.rb b/activesupport/test/weak_hash_test.rb
new file mode 100644
index 0000000000..7d1620dc34
--- /dev/null
+++ b/activesupport/test/weak_hash_test.rb
@@ -0,0 +1,33 @@
+require 'abstract_unit'
+require 'active_support/weak_hash'
+
+class WeakHashTest < ActiveSupport::TestCase
+
+  def setup
+    @weak_hash = ActiveSupport::WeakHash.new
+    @str = "A";
+    @obj = Object.new
+  end
+
+  test "allows us to assign value, and return assigned value" do
+    a = @str; b = @obj
+    assert_equal @weak_hash[a] = b, b
+  end
+
+  test "should allow us to assign and read value" do
+    a = @str; b = @obj
+    assert_equal @weak_hash[a] = b, b
+    assert_equal @weak_hash[a], b
+  end
+
+  test "should use object_id to identify objects" do
+    a = Object.new
+    @weak_hash[a] = "b"
+    assert_nil @weak_hash[a.dup]
+  end
+
+  test "should find objects that have same hash" do
+    @weak_hash["a"] = "b"
+    assert_equal "b", @weak_hash["a"]
+  end
+end