Index: src/Common/utility.h
===================================================================
--- src/Common/utility.h	(revision a5de33ebd685fe6ecb7f95deb3a78328f5b9da15)
+++ src/Common/utility.h	(revision 55a68c3dc9290e2bb34da101039e435d02bc9dea)
@@ -25,4 +25,5 @@
 #include <sstream>
 #include <string>
+#include <type_traits>
 
 #include <cassert>
@@ -305,5 +306,5 @@
 // for ( val : group_iterate( container1, container2, ... ) ) {}
 // syntax to have a for each that iterates multiple containers of the same length
-// TODO: update to use variadic arguments, perfect forwarding
+// TODO: update to use variadic arguments
 
 template< typename T1, typename T2 >
@@ -314,7 +315,9 @@
 
 	struct iterator {
-		typedef std::tuple<typename T1::value_type, typename T2::value_type> value_type;
-		typedef typename T1::iterator T1Iter;
-		typedef typename T2::iterator T2Iter;
+		typedef typename std::remove_reference<T1>::type T1val;
+		typedef typename std::remove_reference<T2>::type T2val;
+		typedef std::tuple<typename T1val::value_type &, typename T2val::value_type &> value_type;
+		typedef typename T1val::iterator T1Iter;
+		typedef typename T2val::iterator T2Iter;
 		typedef std::tuple<T1Iter, T2Iter> IterTuple;
 		IterTuple it;
@@ -324,5 +327,5 @@
 		}
 		bool operator!=( const iterator &other ) const { return it != other.it; }
-		value_type operator*() const { return std::make_tuple( *std::get<0>(it), *std::get<1>(it) ); }
+		value_type operator*() const { return std::tie( *std::get<0>(it), *std::get<1>(it) ); }
 	};
 	iterator begin() { return iterator( std::get<0>(args).begin(), std::get<1>(args).begin() ); }
@@ -334,6 +337,6 @@
 
 template< typename... Args >
-group_iterate_t<Args...> group_iterate( const Args &... args ) {
-	return group_iterate_t<Args...>(args...);
+group_iterate_t<Args...> group_iterate( Args &&... args ) {
+	return group_iterate_t<Args...>(std::forward<Args>( args )...);
 }