From 806a96e42c03a0551bf2b5903d56efc468931711 Mon Sep 17 00:00:00 2001
From: Peter Dimov <pdimov@pdimov.com>
Date: Sun, 22 Oct 2017 01:47:00 +0300
Subject: [PATCH] Add mp_nth_element_q

---
 doc/mp11/algorithm.adoc          | 10 +++++-
 include/boost/mp11/algorithm.hpp |  1 +
 test/Jamfile                     |  1 +
 test/mp_nth_element_q.cpp        | 59 ++++++++++++++++++++++++++++++++
 4 files changed, 70 insertions(+), 1 deletion(-)
 create mode 100644 test/mp_nth_element_q.cpp

diff --git a/doc/mp11/algorithm.adoc b/doc/mp11/algorithm.adoc
index 9ffe45c..fa0dc50 100644
--- a/doc/mp11/algorithm.adoc
+++ b/doc/mp11/algorithm.adoc
@@ -480,7 +480,8 @@ As `mp_sort`, but takes a quoted metafunction.
 
 ## mp_nth_element_c<L, I, P>
 
-    template<class L, std::size_t I, template<class...> class P> using mp_nth_element_c = /*...*/;
+    template<class L, std::size_t I, template<class...> class P> using mp_nth_element_c =
+        /*...*/;
 
 Returns the element at position `I` in `mp_sort<L, P>`.
 
@@ -490,6 +491,13 @@ Returns the element at position `I` in `mp_sort<L, P>`.
 
 Like `mp_nth_element_c`, but with a type argument `I`. `I::value` must be a nonnegative number.
 
+## mp_nth_element_q<L, I, Q>
+
+    template<class L, class I, class Q> using mp_nth_element_q =
+        mp_nth_element<L, I, Q::template fn>;
+
+Like `mp_nth_element`, but takes a quoted metafunction.
+
 ## mp_min_element<L, P>
 
     template<class L, template<class...> class P> using mp_min_element = /*...*/;
diff --git a/include/boost/mp11/algorithm.hpp b/include/boost/mp11/algorithm.hpp
index be94a83..08680b2 100644
--- a/include/boost/mp11/algorithm.hpp
+++ b/include/boost/mp11/algorithm.hpp
@@ -556,6 +556,7 @@ template<template<class...> class L, class T1, class... T, std::size_t I, templa
 
 template<class L, std::size_t I, template<class...> class P> using mp_nth_element_c = typename detail::mp_nth_element_impl<L, I, P>::type;
 template<class L, class I, template<class...> class P> using mp_nth_element = typename detail::mp_nth_element_impl<L, std::size_t{ I::value }, P>::type;
+template<class L, class I, class Q> using mp_nth_element_q = mp_nth_element<L, I, Q::template fn>;
 
 // mp_find<L, V>
 namespace detail
diff --git a/test/Jamfile b/test/Jamfile
index eebca65..ba4a16d 100644
--- a/test/Jamfile
+++ b/test/Jamfile
@@ -87,6 +87,7 @@ run mp_from_sequence.cpp ;
 run mp_min_element.cpp ;
 run mp_max_element.cpp ;
 run mp_nth_element.cpp ;
+run mp_nth_element_q.cpp ;
 
 # integral
 run integral.cpp ;
diff --git a/test/mp_nth_element_q.cpp b/test/mp_nth_element_q.cpp
new file mode 100644
index 0000000..0c6a333
--- /dev/null
+++ b/test/mp_nth_element_q.cpp
@@ -0,0 +1,59 @@
+
+// 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/mp11/algorithm.hpp>
+#include <boost/mp11/list.hpp>
+#include <boost/mp11/integral.hpp>
+#include <boost/mp11/function.hpp>
+#include <boost/mp11/utility.hpp>
+#include <boost/core/lightweight_test_trait.hpp>
+#include <type_traits>
+#include <tuple>
+
+int main()
+{
+    using boost::mp11::mp_nth_element_q;
+    using boost::mp11::mp_list_c;
+    using boost::mp11::mp_sort_q;
+    using boost::mp11::mp_less;
+    using boost::mp11::mp_at_c;
+    using boost::mp11::mp_size_t;
+    using boost::mp11::mp_rename;
+    using boost::mp11::mp_quote;
+
+    using Q_less = mp_quote<mp_less>;
+
+    {
+        using L1 = mp_list_c<int, 7, 1, 11, 3, 2, 2, 4>;
+        using L2 = mp_sort_q<L1, Q_less>;
+
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_nth_element_q<L1, mp_size_t<0>, Q_less>, mp_at_c<L2, 0>>));
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_nth_element_q<L1, mp_size_t<1>, Q_less>, mp_at_c<L2, 1>>));
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_nth_element_q<L1, mp_size_t<2>, Q_less>, mp_at_c<L2, 2>>));
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_nth_element_q<L1, mp_size_t<3>, Q_less>, mp_at_c<L2, 3>>));
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_nth_element_q<L1, mp_size_t<4>, Q_less>, mp_at_c<L2, 4>>));
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_nth_element_q<L1, mp_size_t<5>, Q_less>, mp_at_c<L2, 5>>));
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_nth_element_q<L1, mp_size_t<6>, Q_less>, mp_at_c<L2, 6>>));
+    }
+
+    {
+        using L1 = mp_rename<mp_list_c<int, 7, 1, 11, 3, 2, 2, 4>, std::tuple>;
+        using L2 = mp_sort_q<L1, Q_less>;
+
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_nth_element_q<L1, mp_size_t<0>, Q_less>, mp_at_c<L2, 0>>));
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_nth_element_q<L1, mp_size_t<1>, Q_less>, mp_at_c<L2, 1>>));
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_nth_element_q<L1, mp_size_t<2>, Q_less>, mp_at_c<L2, 2>>));
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_nth_element_q<L1, mp_size_t<3>, Q_less>, mp_at_c<L2, 3>>));
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_nth_element_q<L1, mp_size_t<4>, Q_less>, mp_at_c<L2, 4>>));
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_nth_element_q<L1, mp_size_t<5>, Q_less>, mp_at_c<L2, 5>>));
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_nth_element_q<L1, mp_size_t<6>, Q_less>, mp_at_c<L2, 6>>));
+    }
+
+    return boost::report_errors();
+}