add fetch

lib/memcached/rails.rb

@@ -98,6 +98,17 @@ class Memcached
       set(key, value, options[:ttl] || @default_ttl, options[:raw])
     end
 
+    def fetch(key, options={})
+      result = read(key, options)
+      if result.nil?
+        result = yield
+        write(key, result, options)
+        result
+      else
+        result
+      end
+    end
+
     # Wraps Memcached#add so that it doesn't raise.
     def add(key, value, ttl=@default_ttl, raw=false)
       super(key, value, ttl, !raw)

test/unit/rails_test.rb

@@ -175,6 +175,21 @@ class RailsTest < Test::Unit::TestCase
     assert_equal @value, result
   end
 
+  def test_fetch
+    # returns
+    assert_equal @value, @cache.fetch("x"){ @value }
+
+    # sets
+    assert_equal @value, @cache.read("x")
+
+    # reads
+    assert_equal @value, @cache.fetch("x"){ 1 }
+
+    # works with options
+    @cache.expects(:write).with("y", 1, :foo => :bar)
+    @cache.fetch("y", :foo => :bar){ 1 }
+  end
+
   private
 
   def key