diff --git a/src/util/optional.hpp b/src/util/optional.hpp index 11abdc551ade3b4788ac6a4a3aa64d1400b1c937..7405f8306abf95ffb2b14db77b21f58c9ec23dd1 100644 --- a/src/util/optional.hpp +++ b/src/util/optional.hpp @@ -334,7 +334,7 @@ struct optional<X&>: detail::optional_base<X&> { template < typename Y, - typename = typename std::enable_if<!detail::is_optional<Y>::value>> + typename = typename std::enable_if<!detail::is_optional<Y>::value>::type> optional& operator=(Y& y) { set = true; ref() = y;