From 66c758f13aeda9cec817548cd7a8c4f6d1af324a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Kjist=C3=B3f?= <mrtoth@strongds.hu>
Date: Sat, 3 Dec 2016 18:44:09 +0100
Subject: [PATCH] implemented a SFINAE compile-time checker for receive
 policies

---
 check_policy.hpp | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)
 create mode 100644 check_policy.hpp

diff --git a/check_policy.hpp b/check_policy.hpp
new file mode 100644
index 0000000..201c2ad
--- /dev/null
+++ b/check_policy.hpp
@@ -0,0 +1,24 @@
+#pragma once
+#include <type_traits>
+#include "chat_messages.hpp"
+
+
+
+/* SFINAE compile-type checker for receive policies (as defined in chat_networking.hpp)
+ * it checks whether PolicyCandidate supplies all of the following methods:
+ *      - void message_do_what(chat_message)                                         */
+template <class PolicyCandidate, typename = void>
+struct is_valid_policy : std::false_type {};
+
+template <class PolicyCandidate>
+struct is_valid_policy<
+        PolicyCandidate,
+        typename
+        std::enable_if<
+                std::is_same<
+                        decltype(PolicyCandidate
+                                 ::message_do_what(std::declval<chat::chat_message>())),
+                        void
+                >::value
+        >::type>
+: std::true_type {};
\ No newline at end of file