From 7100d10c7e359205648f2737f0d2b42c9657daa8 Mon Sep 17 00:00:00 2001
From: Peter Dimov <pdimov@pdimov.com>
Date: Fri, 19 May 2017 15:37:49 +0300
Subject: [PATCH] Make mp_infoke SFINAE-friendly

---
 include/boost/mp11/utility.hpp | 15 ++++++++++-----
 test/Jamfile.v2                |  1 +
 test/mp_invoke_sf.cpp          | 33 +++++++++++++++++++++++++++++++++
 3 files changed, 44 insertions(+), 5 deletions(-)
 create mode 100644 test/mp_invoke_sf.cpp

diff --git a/include/boost/mp11/utility.hpp b/include/boost/mp11/utility.hpp
index 1439596..dd85e89 100644
--- a/include/boost/mp11/utility.hpp
+++ b/include/boost/mp11/utility.hpp
@@ -116,19 +116,24 @@ template<template<class...> class F> struct mp_quote
     template<class... T> using fn = typename mp_defer<F, T...>::type;
 };
 
-// mp_unquote
+// mp_invoke
+#if BOOST_WORKAROUND( BOOST_MSVC, < 1900 )
+
 namespace detail
 {
 
-template<class Q, class... T> struct mp_invoke_impl
-{
-    using type = typename Q::template fn<T...>;
-};
+template<class Q, class... T> struct mp_invoke_impl: mp_defer<Q::template fn, T...> {};
 
 } // namespace detail
 
 template<class Q, class... T> using mp_invoke = typename detail::mp_invoke_impl<Q, T...>::type;
 
+#else
+
+template<class Q, class... T> using mp_invoke = typename Q::template fn<T...>;
+
+#endif
+
 } // namespace mp11
 } // namespace boost
 
diff --git a/test/Jamfile.v2 b/test/Jamfile.v2
index f45c9e6..e700170 100644
--- a/test/Jamfile.v2
+++ b/test/Jamfile.v2
@@ -83,6 +83,7 @@ run mp_valid.cpp : : : $(REQ) ;
 run mp_defer.cpp : : : $(REQ) ;
 run mp_quote.cpp : : : $(REQ) ;
 run mp_invoke.cpp : : : $(REQ) ;
+run mp_invoke_sf.cpp : : : $(REQ) ;
 
 # integer_sequence
 run integer_sequence.cpp : : : $(REQ) ;
diff --git a/test/mp_invoke_sf.cpp b/test/mp_invoke_sf.cpp
new file mode 100644
index 0000000..7c2feb6
--- /dev/null
+++ b/test/mp_invoke_sf.cpp
@@ -0,0 +1,33 @@
+
+// Copyright 2015, 2017 Peter Dimov.
+//
+// Distributed under the Boost Software License, Version 1.0.
+//
+// See accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt
+
+
+#include <boost/mp11/utility.hpp>
+#include <boost/core/lightweight_test_trait.hpp>
+#include <type_traits>
+
+using boost::mp11::mp_invoke;
+using boost::mp11::mp_quote;
+using boost::mp11::mp_valid;
+using boost::mp11::mp_identity_t;
+
+int main()
+{
+    BOOST_TEST_TRAIT_FALSE((mp_valid<mp_invoke>));
+    BOOST_TEST_TRAIT_FALSE((mp_valid<mp_invoke, void>));
+    BOOST_TEST_TRAIT_FALSE((mp_valid<mp_invoke, void, void>));
+    BOOST_TEST_TRAIT_FALSE((mp_valid<mp_invoke, void, void, void>));
+
+    using Qi = mp_quote<mp_identity_t>;
+
+    BOOST_TEST_TRAIT_FALSE((mp_valid<mp_invoke, Qi>));
+    BOOST_TEST_TRAIT_TRUE((mp_valid<mp_invoke, Qi, void>));
+    BOOST_TEST_TRAIT_FALSE((mp_valid<mp_invoke, Qi, void, void>));
+
+    return boost::report_errors();
+}