Add mp_back, mp_pop_back

test/mp_back.cpp

@@ -0,0 +1,52 @@
+
+// Copyright 2015, 2019 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/core/lightweight_test_trait.hpp>
+#include <boost/mp11/algorithm.hpp>
+#include <boost/mp11/list.hpp>
+#include <boost/mp11/utility.hpp>
+#include <type_traits>
+#include <tuple>
+#include <utility>
+
+int main()
+{
+    using boost::mp11::mp_list;
+    using boost::mp11::mp_back;
+
+    using L1 = mp_list<void>;
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_back<L1>, void>));
+
+    using L2 = mp_list<float, void, int[]>;
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_back<L2>, int[]>));
+
+    using L3 = std::tuple<int>;
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_back<L3>, int>));
+
+    using L4 = std::pair<char, double>;
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_back<L4>, double>));
+
+    using L5 = std::add_const<void()>;
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_back<L5>, void()>));
+
+    using boost::mp11::mp_iota_c;
+    using boost::mp11::mp_size_t;
+
+    int const N = 137;
+
+    using L6 = mp_iota_c<N>;
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_back<L6>, mp_size_t<N-1>>));
+
+    using boost::mp11::mp_valid;
+
+    using L7 = mp_list<>;
+    BOOST_TEST_TRAIT_FALSE((mp_valid<mp_back, L7>));
+
+    return boost::report_errors();
+}