1.1 --- a/lemon/concepts/maps.h	Sun Oct 04 10:15:32 2009 +0200
     1.2 +++ b/lemon/concepts/maps.h	Wed Dec 09 11:14:06 2009 +0100
     1.3 @@ -182,7 +182,8 @@
     1.4  
     1.5        template<typename _ReferenceMap>
     1.6        struct Constraints {
     1.7 -        void constraints() {
     1.8 +        typename enable_if<typename _ReferenceMap::ReferenceMapTag, void>::type
     1.9 +        constraints() {
    1.10            checkConcept<ReadWriteMap<K, T>, _ReferenceMap >();
    1.11            ref = m[key];
    1.12            m[key] = val;