add the fetch method to sessions

actionpack/CHANGELOG.md

@@ -1,3 +1,15 @@
+*   Add `session#fetch` method
+
+    fetch behaves like [Hash#fetch](http://www.ruby-doc.org/core-1.9.3/Hash.html#method-i-fetch).  
+    It returns a value from the hash for the given key.
+    If the key can’t be found, there are several options:
+
+      * With no other arguments, it will raise an KeyError exception.
+      * If a default value is given, then that will be returned.
+      * If the optional code block is specified, then that will be run and its result returned.
+
+    *Damien Mathieu*
+
 *   Don't let strong parameters mutate the given hash via `fetch`
 
     Create a new instance if the given parameter is a `Hash` instead of

actionpack/lib/action_dispatch/request/session.rb

@@ -127,6 +127,18 @@ module ActionDispatch
         @delegate.delete key.to_s
       end
 
+      def fetch(key, default=nil)
+        if self.key?(key)
+          self[key]
+        elsif default
+          self[key] = default
+        elsif block_given?
+          self[key] = yield(key)
+        else
+          raise KeyError
+        end
+      end
+
       def inspect
         if loaded?
           super

actionpack/test/dispatch/request/session_test.rb

@@ -61,6 +61,19 @@ module ActionDispatch
         assert_equal([], s.values)
       end
 
+      def test_fetch
+        session = Session.create(store, {}, {})
+        session['one'] = '1'
+
+        assert_equal '1', session.fetch(:one)
+        assert_equal '2', session.fetch(:two, '2')
+        assert_equal 'three', session.fetch(:three) {|el| el.to_s }
+
+        assert_raise KeyError do
+          session.fetch(:four)
+        end
+      end
+
       private
       def store
         Class.new {