From 3bfc1784ad7609e6d3aec2f5e422528f7b0a67e5 Mon Sep 17 00:00:00 2001
From: Brian McKinnon <bpmckinnon@gmail.com>
Date: Sat, 2 May 2020 21:23:59 -0500
Subject: [PATCH] Fix compiler error for is_invocable is a c++17 feature

---
 parallel_hashmap/phmap.h | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/parallel_hashmap/phmap.h b/parallel_hashmap/phmap.h
index b89393e..0a38a7d 100644
--- a/parallel_hashmap/phmap.h
+++ b/parallel_hashmap/phmap.h
@@ -3394,8 +3394,8 @@ public:
     }
 
     template <class K = key_type, class V = mapped_type>
-    std::enable_if_t<std::is_assignable<mapped_type&, V>::value, 
-        bool> if_contains(const key_arg<K>& key, V& v) const {
+    std::enable_if_t<std::is_assignable<mapped_type&, V>::value 
+        , bool> if_contains(const key_arg<K>& key, V& v) const {
         typename Lockable::SharedLock m;
         auto it = const_cast<parallel_hash_map *>(this)->find(key, this->hash(key), m);
         if (it == this->end())
@@ -3405,8 +3405,11 @@ public:
     }
 
     template <class K = key_type, class F>
-    std::enable_if_t<!std::is_assignable<mapped_type&, F>::value && std::is_invocable<F, mapped_type&>::value,
-        bool> if_contains(const key_arg<K>& key, F&& f) const {
+    std::enable_if_t<!std::is_assignable<mapped_type&, F>::value
+#if __cplusplus >= 201703L
+        && std::is_invocable<F, mapped_type&>::value
+#endif
+        , bool> if_contains(const key_arg<K>& key, F&& f) const {
         typename Lockable::SharedLock m;
         auto it = const_cast<parallel_hash_map*>(this)->find(key, this->hash(key), m);
         if (it == this->end())