Add mp_drop.

include/boost/mp11/algorithm.hpp

@@ -10,6 +10,7 @@
 
 #include <boost/mp11/list.hpp>
 #include <boost/mp11/integral.hpp>
+#include <boost/mp11/utility.hpp>
 #include <boost/mp11/detail/mp_plus.hpp>
 #include <boost/config.hpp>
 #include <boost/detail/workaround.hpp>
@@ -199,7 +200,6 @@ template<class L, std::size_t N> using mp_repeat_c = typename detail::mp_repeat_
 template<class L, class N> using mp_repeat = typename detail::mp_repeat_impl<L, N>::type;
 
 // mp_product<F, L...>
-
 namespace detail
 {
 
@@ -227,6 +227,26 @@ template<template<class...> class F, class L1, class... L> struct mp_product_imp
 template<template<class...> class F, class... L> using mp_product = typename detail::mp_product_impl<F, L...>::type;
 
 // mp_drop(_c)<L, N>
+namespace detail
+{
+
+template<class L, class L2> struct mp_drop_impl;
+
+template<template<class...> class L, class... T, template<class...> class L2, class... U> struct mp_drop_impl<L<T...>, L2<U...>>
+{
+    template<class... W> static mp_identity<L<W...>> f( U*..., mp_identity<W>*... );
+
+    using R = decltype( f( (mp_identity<T>*)0 ... ) );
+
+    using type = typename R::type;
+};
+
+} // namespace detail
+
+template<class L, std::size_t N> using mp_drop_c = typename detail::mp_drop_impl<L, mp_repeat_c<mp_list<void>, N>>::type;
+
+template<class L, class N> using mp_drop = typename detail::mp_drop_impl<L, mp_repeat<mp_list<void>, N>>::type;
+
 // mp_take(_c)<L, N>
 // mp_at(_c)<L, I>
 // mp_find<L, V>

test/Jamfile.v2

@@ -34,6 +34,7 @@ run mp_count_if.cpp : : : $(REQ) ;
 run mp_contains.cpp : : : $(REQ) ;
 run mp_repeat.cpp : : : $(REQ) ;
 run mp_product.cpp : : : $(REQ) ;
+run mp_drop.cpp : : : $(REQ) ;
 
 # integral
 run integral.cpp : : : $(REQ) ;

test/mp_drop.cpp

@@ -0,0 +1,85 @@
+
+//  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/algorithm.hpp>
+#include <boost/mp11/list.hpp>
+#include <boost/mp11/integral.hpp>
+#include <boost/core/lightweight_test_trait.hpp>
+#include <type_traits>
+#include <tuple>
+#include <utility>
+
+struct X1 {};
+struct X2 {};
+struct X3 {};
+struct X4 {};
+struct X5 {};
+
+int main()
+{
+    using boost::mp_list;
+    using boost::mp_drop;
+    using boost::mp_drop_c;
+    using boost::mp_size_t;
+
+    {
+        using L1 = mp_list<>;
+
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_drop_c<L1, 0>, L1>));
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_drop<L1, mp_size_t<0>>, L1>));
+
+        using L2 = mp_list<X1, X2, X3, X4, X5>;
+
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_drop_c<L2, 0>, mp_list<X1, X2, X3, X4, X5>>));
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_drop_c<L2, 1>, mp_list<X2, X3, X4, X5>>));
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_drop_c<L2, 2>, mp_list<X3, X4, X5>>));
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_drop_c<L2, 3>, mp_list<X4, X5>>));
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_drop_c<L2, 4>, mp_list<X5>>));
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_drop_c<L2, 5>, mp_list<>>));
+
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_drop<L2, mp_size_t<0>>, mp_list<X1, X2, X3, X4, X5>>));
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_drop<L2, mp_size_t<1>>, mp_list<X2, X3, X4, X5>>));
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_drop<L2, mp_size_t<2>>, mp_list<X3, X4, X5>>));
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_drop<L2, mp_size_t<3>>, mp_list<X4, X5>>));
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_drop<L2, mp_size_t<4>>, mp_list<X5>>));
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_drop<L2, mp_size_t<5>>, mp_list<>>));
+    }
+
+    {
+        using L1 = std::tuple<>;
+
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_drop_c<L1, 0>, L1>));
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_drop<L1, mp_size_t<0>>, L1>));
+
+        using L2 = std::tuple<X1, X2, X3, X4, X5>;
+
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_drop_c<L2, 0>, std::tuple<X1, X2, X3, X4, X5>>));
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_drop_c<L2, 1>, std::tuple<X2, X3, X4, X5>>));
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_drop_c<L2, 2>, std::tuple<X3, X4, X5>>));
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_drop_c<L2, 3>, std::tuple<X4, X5>>));
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_drop_c<L2, 4>, std::tuple<X5>>));
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_drop_c<L2, 5>, std::tuple<>>));
+
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_drop<L2, mp_size_t<0>>, std::tuple<X1, X2, X3, X4, X5>>));
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_drop<L2, mp_size_t<1>>, std::tuple<X2, X3, X4, X5>>));
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_drop<L2, mp_size_t<2>>, std::tuple<X3, X4, X5>>));
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_drop<L2, mp_size_t<3>>, std::tuple<X4, X5>>));
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_drop<L2, mp_size_t<4>>, std::tuple<X5>>));
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_drop<L2, mp_size_t<5>>, std::tuple<>>));
+    }
+
+    {
+        using L1 = std::pair<X1, X2>;
+
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_drop_c<L1, 0>, L1>));
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_drop<L1, mp_size_t<0>>, L1>));
+    }
+
+    return boost::report_errors();
+}