From 0837acfde123725962ee5d4220aa63b48dd9eef7 Mon Sep 17 00:00:00 2001
From: Peter Dimov <pdimov@gmail.com>
Date: Fri, 12 Mar 2021 06:18:45 +0200
Subject: [PATCH] Add mp_split (refs #59)

---
 include/boost/mp11/algorithm.hpp | 23 ++++++++++++++
 test/Jamfile                     |  1 +
 test/mp_split.cpp                | 51 ++++++++++++++++++++++++++++++++
 3 files changed, 75 insertions(+)
 create mode 100644 test/mp_split.cpp

diff --git a/include/boost/mp11/algorithm.hpp b/include/boost/mp11/algorithm.hpp
index f936a67..40a8c55 100644
--- a/include/boost/mp11/algorithm.hpp
+++ b/include/boost/mp11/algorithm.hpp
@@ -1240,6 +1240,7 @@ template<class L, class Q> using mp_pairwise_fold_impl = mp_transform_q<Q, mp_po
 template<class L, class Q> using mp_pairwise_fold_q = mp_eval_if<mp_empty<L>, mp_clear<L>, detail::mp_pairwise_fold_impl, L, Q>;
 template<class L, template<class...> class F> using mp_pairwise_fold = mp_pairwise_fold_q<L, mp_quote<F>>;
 
+// mp_intersperse<L, S>
 namespace detail
 {
 
@@ -1273,6 +1274,28 @@ template<template<class...> class L, class T1, class... T, class S> struct mp_in
 
 template<class L, class S> using mp_intersperse = typename detail::mp_intersperse_impl<L, S>::type;
 
+// mp_split<L, S>
+namespace detail
+{
+
+template<class L, class S, class J> struct mp_split_impl;
+
+} // namespace detail
+
+template<class L, class S> using mp_split = typename detail::mp_split_impl<L, S, mp_find<L, S>>::type;
+
+namespace detail
+{
+
+template<class L, class S, class J> using mp_split_impl_ = mp_push_front<mp_split<mp_drop_c<L, J::value + 1>, S>, mp_take<L, J>>;
+
+template<class L, class S, class J> struct mp_split_impl
+{
+    using type = mp_eval_if_c<mp_size<L>::value == J::value, mp_push_back<mp_clear<L>, L>, mp_split_impl_, L, S, J>;
+};
+
+} // namespace detail
+
 } // namespace mp11
 } // namespace boost
 
diff --git a/test/Jamfile b/test/Jamfile
index 25e7d6b..531e598 100644
--- a/test/Jamfile
+++ b/test/Jamfile
@@ -125,6 +125,7 @@ run mp_iterate.cpp ;
 run mp_pairwise_fold.cpp ;
 run mp_pairwise_fold_q.cpp ;
 run mp_intersperse.cpp ;
+run mp_split.cpp ;
 
 # integral
 run integral.cpp ;
diff --git a/test/mp_split.cpp b/test/mp_split.cpp
new file mode 100644
index 0000000..0cea072
--- /dev/null
+++ b/test/mp_split.cpp
@@ -0,0 +1,51 @@
+// Copyright 2021 Peter Dimov
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/mp11/algorithm.hpp>
+#include <boost/mp11/list.hpp>
+#include <boost/core/lightweight_test_trait.hpp>
+#include <type_traits>
+#include <tuple>
+#include <utility>
+
+struct X1 {};
+struct X2 {};
+struct X3 {};
+struct X4 {};
+
+struct S {};
+
+int main()
+{
+    using boost::mp11::mp_list;
+    using boost::mp11::mp_split;
+
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_split<mp_list<>, void>, mp_list<mp_list<>>>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_split<mp_list<X1>, void>, mp_list<mp_list<X1>>>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_split<mp_list<X1, X2>, void>, mp_list<mp_list<X1, X2>>>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_split<mp_list<X1, X2, X3>, void>, mp_list<mp_list<X1, X2, X3>>>));
+
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_split<mp_list<S>, S>, mp_list<mp_list<>, mp_list<>>>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_split<mp_list<S, S>, S>, mp_list<mp_list<>, mp_list<>, mp_list<>>>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_split<mp_list<S, S, S>, S>, mp_list<mp_list<>, mp_list<>, mp_list<>, mp_list<>>>));
+
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_split<mp_list<X1, S, X2>, S>, mp_list<mp_list<X1>, mp_list<X2>>>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_split<mp_list<X1, X2, S, X3, X4>, S>, mp_list<mp_list<X1, X2>, mp_list<X3, X4>>>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_split<mp_list<S, X1, X2, S, S, X3, X4, S>, S>, mp_list<mp_list<>, mp_list<X1, X2>, mp_list<>, mp_list<X3, X4>, mp_list<>>>));
+
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_split<std::tuple<>, void>, std::tuple<std::tuple<>>>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_split<std::tuple<X1>, void>, std::tuple<std::tuple<X1>>>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_split<std::tuple<X1, X2>, void>, std::tuple<std::tuple<X1, X2>>>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_split<std::tuple<X1, X2, X3>, void>, std::tuple<std::tuple<X1, X2, X3>>>));
+
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_split<std::tuple<S>, S>, std::tuple<std::tuple<>, std::tuple<>>>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_split<std::tuple<S, S>, S>, std::tuple<std::tuple<>, std::tuple<>, std::tuple<>>>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_split<std::tuple<S, S, S>, S>, std::tuple<std::tuple<>, std::tuple<>, std::tuple<>, std::tuple<>>>));
+
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_split<std::tuple<X1, S, X2>, S>, std::tuple<std::tuple<X1>, std::tuple<X2>>>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_split<std::tuple<X1, X2, S, X3, X4>, S>, std::tuple<std::tuple<X1, X2>, std::tuple<X3, X4>>>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_split<std::tuple<S, X1, X2, S, S, X3, X4, S>, S>, std::tuple<std::tuple<>, std::tuple<X1, X2>, std::tuple<>, std::tuple<X3, X4>, std::tuple<>>>));
+
+    return boost::report_errors();
+}