function_traits<>: define as empty by default

An incomplete type was preventing some SFINAE cases for literal types.

1 files changed, 1 insertions, 1 deletions

diff --git a/lib/util.h b/lib/util.h
index 8c92df74..34f8714a 100644
--- a/lib/util.h
+++ b/lib/util.h
@@ -148,7 +148,7 @@ public:
 
 namespace _impl {
     template <typename AlwaysVoid, typename>
-    struct fn_traits;
+    struct fn_traits {};
 }
 
 /// Determine traits of an arbitrary function/lambda/functor