1 files changed, 2 insertions, 0 deletions
diff --git a/lib/util.h b/lib/util.h
index c6171b91..9c146100 100644
--- a/lib/util.h
+++ b/lib/util.h
@@ -138,6 +138,8 @@ public:
     const value_type& operator*() const& { return base_type::operator*(); }
     value_type& operator*() && { return base_type::operator*(); }
 };
+template <typename T>
+Omittable(T&&) -> Omittable<T>;
 
 namespace _impl {
     template <typename T>