From 28c420edf7fa87a539da48203b6e061bd2d4a00e Mon Sep 17 00:00:00 2001
From: Peter Dimov <pdimov@pdimov.com>
Date: Sat, 1 Apr 2017 20:01:51 +0300
Subject: [PATCH] Add mp_same.

---
 include/boost/mp11/function.hpp | 21 +++++++++++++++++++++
 test/Jamfile.v2                 |  1 +
 test/mp_same.cpp                | 33 +++++++++++++++++++++++++++++++++
 3 files changed, 55 insertions(+)
 create mode 100644 test/mp_same.cpp

diff --git a/include/boost/mp11/function.hpp b/include/boost/mp11/function.hpp
index e714aa0..571a24b 100644
--- a/include/boost/mp11/function.hpp
+++ b/include/boost/mp11/function.hpp
@@ -12,6 +12,7 @@
 #include <boost/mp11/utility.hpp>
 #include <boost/mp11/detail/mp_list.hpp>
 #include <boost/mp11/detail/mp_count.hpp>
+#include <type_traits>
 
 namespace boost
 {
@@ -84,6 +85,26 @@ template<class T1, class... T> struct mp_or_impl<T1, T...>
 
 } // namespace detail
 
+// mp_same<T...>
+namespace detail
+{
+
+template<class... T> struct mp_same_impl;
+
+template<> struct mp_same_impl<>
+{
+    using type = mp_true;
+};
+
+template<class T1, class... T> struct mp_same_impl<T1, T...>
+{
+    using type = mp_all<std::is_same<T1, T>...>;
+};
+
+} // namespace detail
+
+template<class... T> using mp_same = typename detail::mp_same_impl<T...>::type;
+
 } // namespace mp11
 } // namespace boost
 
diff --git a/test/Jamfile.v2 b/test/Jamfile.v2
index cfc1c36..3bfaec6 100644
--- a/test/Jamfile.v2
+++ b/test/Jamfile.v2
@@ -94,6 +94,7 @@ run mp_all.cpp : : : $(REQ) ;
 run mp_and.cpp : : : $(REQ) ;
 run mp_any.cpp : : : $(REQ) ;
 run mp_or.cpp : : : $(REQ) ;
+run mp_same.cpp : : : $(REQ) ;
 
 # map
 run mp_map_find.cpp : : : $(REQ) ;
diff --git a/test/mp_same.cpp b/test/mp_same.cpp
new file mode 100644
index 0000000..5b642ae
--- /dev/null
+++ b/test/mp_same.cpp
@@ -0,0 +1,33 @@
+
+// Copyright 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/function.hpp>
+#include <boost/core/lightweight_test_trait.hpp>
+#include <type_traits>
+
+int main()
+{
+    using boost::mp11::mp_same;
+    using boost::mp11::mp_true;
+    using boost::mp11::mp_false;
+
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_same<>, mp_true>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_same<void>, mp_true>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_same<void, void>, mp_true>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_same<void, void, void>, mp_true>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_same<void, void, void, void>, mp_true>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_same<void, void, void, void, void>, mp_true>));
+
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_same<void, int>, mp_false>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_same<void, void, int>, mp_false>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_same<void, void, void, int>, mp_false>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_same<void, void, void, void, int>, mp_false>));
+
+    return boost::report_errors();
+}