Add make_from_tuple

test/make_from_tuple_cx.cpp

@@ -0,0 +1,76 @@
+
+//  Copyright 2015 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/tuple.hpp>
+#include <boost/config.hpp>
+
+// Technically std::tuple isn't constexpr enabled in C++11, but it works with libstdc++
+
+#if defined( BOOST_NO_CXX11_CONSTEXPR ) || ( defined( _LIBCPP_VERSION ) && __cplusplus < 201400L )
+
+int main() {}
+
+#else
+
+#include <tuple>
+#include <array>
+#include <utility>
+
+struct T1
+{
+    int x, y, z;
+
+    constexpr T1( int x = 0, int y = 0, int z = 0 ): x(x), y(y), z(z) {}
+};
+
+int main()
+{
+    using boost::mp11::make_from_tuple;
+
+    {
+        constexpr std::tuple<int, short, char> tp{ 1, 2, 3 };
+
+        constexpr auto r = make_from_tuple<T1>( tp );
+
+        static_assert( r.x == 1, "r.x == 1" );
+        static_assert( r.y == 2, "r.y == 2" );
+        static_assert( r.z == 3, "r.z == 3" );
+    }
+
+    {
+        constexpr std::pair<short, char> tp{ 1, 2 };
+
+        constexpr auto r = make_from_tuple<T1>( tp );
+
+        static_assert( r.x == 1, "r.x == 1" );
+        static_assert( r.y == 2, "r.y == 2" );
+        static_assert( r.z == 0, "r.z == 0" );
+    }
+
+    {
+        constexpr std::array<short, 3> tp{{ 1, 2, 3 }};
+
+        constexpr auto r = make_from_tuple<T1>( tp );
+
+        static_assert( r.x == 1, "r.x == 1" );
+        static_assert( r.y == 2, "r.y == 2" );
+        static_assert( r.z == 3, "r.z == 3" );
+    }
+
+    {
+        constexpr std::tuple<> tp;
+
+        constexpr auto r = make_from_tuple<T1>( tp );
+
+        static_assert( r.x == 0, "r.x == 0" );
+        static_assert( r.y == 0, "r.y == 0" );
+        static_assert( r.z == 0, "r.z == 0" );
+    }
+}
+
+#endif