Make mp_for_each constexpr under C++14

test/mp_for_index_cx.cpp

@@ -0,0 +1,41 @@
+
+// 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/config.hpp>
+
+#if defined( BOOST_NO_CXX14_CONSTEXPR )
+
+int main() {}
+
+#else
+
+#include <boost/mp11/algorithm.hpp>
+#include <boost/core/lightweight_test.hpp>
+#include <boost/config.hpp>
+#include <boost/detail/workaround.hpp>
+
+using boost::mp11::mp_size_t;
+using boost::mp11::mp_for_index;
+
+struct F
+{
+    template<std::size_t I> constexpr std::size_t operator()( mp_size_t<I> ) const
+    {
+        return I;
+    }
+};
+
+#define STATIC_ASSERT(...) static_assert(__VA_ARGS__, #__VA_ARGS__)
+
+int main()
+{
+    constexpr std::size_t i = mp_for_index<64>( 57, F{} );
+    STATIC_ASSERT( i == 57 );
+}
+
+#endif