From acad8b1a61849834fb75722899484e8150422420 Mon Sep 17 00:00:00 2001
From: Philip Top <top1@llnl.gov>
Date: Thu, 19 Dec 2019 12:22:42 -0800
Subject: [PATCH] add additional check for invocability

---
 toml/traits.hpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/toml/traits.hpp b/toml/traits.hpp
index a1c6144..3839451 100644
--- a/toml/traits.hpp
+++ b/toml/traits.hpp
@@ -282,7 +282,7 @@ using enable_if_t = typename std::enable_if<B, T>::type;
 // ---------------------------------------------------------------------------
 // return_type_of_t
 
-#if __cplusplus >= 201703L
+#if __cplusplus >= 201703L && defined(__cpp_lib_is_invocable) && __cpp_lib_is_invokable>=201710
 
 template<typename F, typename ... Args>
 using return_type_of_t = std::invoke_result_t<F, Args...>;