Add mp_min_element, mp_max_element

doc/mp11/algorithm.adoc

@@ -441,6 +441,22 @@ using L1 = mp_list<std::ratio<1,2>, std::ratio<1,4>>;
 using R1 = mp_sort<L1, std::ratio_less>; // mp_list<ratio<1,4>, ratio<1,2>>
 ----
 
+## mp_min_element<L, P>
+
+    template<class L, template<class...> class P> using mp_min_element = /*...*/;
+
+`mp_min_element<L, P>` returns the minimal element of the list `L` according to the ordering `mp_to_bool<P<T, U>>`.
+
+It's equivalent to `mp_fold<mp_rest<L>, mp_first<L>, Q>`, where `Q<T, U>` returns `mp_if<P<T, U>, T, U>`.
+
+## mp_max_element<L, P>
+
+    template<class L, template<class...> class P> using mp_max_element = /*...*/;
+
+`mp_max_element<L, P>` returns the maximal element of the list `L` according to the ordering `mp_to_bool<P<T, U>>`.
+
+It's equivalent to `mp_fold<mp_rest<L>, mp_first<L>, Q>`, where `Q<T, U>` returns `mp_if<P<U, T>, T, U>`.
+
 ## mp_find<L, V>
 
     template<class L, class V> using mp_find = /*...*/;

include/boost/mp11/algorithm.hpp

@@ -922,6 +922,32 @@ template<class L, class I, class J> using mp_erase = mp_append<mp_take<L, I>, mp
 // mp_erase_c<L, I, J>
 template<class L, std::size_t I, std::size_t J> using mp_erase_c = mp_append<mp_take_c<L, I>, mp_drop_c<L, J>>;
 
+// mp_min_element<L, P>
+namespace detail
+{
+
+template<template<class...> class P> struct select_min
+{
+    template<class T1, class T2> using fn = mp_if<P<T1, T2>, T1, T2>;
+};
+
+} // namespace detail
+
+template<class L, template<class...> class P> using mp_min_element = mp_fold_q<mp_rest<L>, mp_first<L>, detail::select_min<P>>;
+
+// mp_max_element<L, P>
+namespace detail
+{
+
+template<template<class...> class P> struct select_max
+{
+    template<class T1, class T2> using fn = mp_if<P<T2, T1>, T1, T2>;
+};
+
+} // namespace detail
+
+template<class L, template<class...> class P> using mp_max_element = mp_fold_q<mp_rest<L>, mp_first<L>, detail::select_max<P>>;
+
 } // namespace mp11
 } // namespace boost
 

test/Jamfile

@@ -78,6 +78,8 @@ run mp_erase.cpp ;
 run mp_with_index.cpp ;
 run mp_with_index_cx.cpp ;
 run mp_from_sequence.cpp ;
+run mp_min_element.cpp ;
+run mp_max_element.cpp ;
 
 # integral
 run integral.cpp ;

test/mp_max_element.cpp

@@ -0,0 +1,55 @@
+
+// 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/core/lightweight_test_trait.hpp>
+#include <type_traits>
+#include <tuple>
+
+using boost::mp11::mp_bool;
+
+template<class T, class U> using sizeof_less = mp_bool<(sizeof(T) < sizeof(U))>;
+
+int main()
+{
+    using boost::mp11::mp_list;
+    using boost::mp11::mp_max_element;
+
+    {
+        using L1 = mp_list<void>;
+
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_max_element<L1, sizeof_less>, void>));
+
+        using L2 = mp_list<char[2], char[4], char[3], char[1]>;
+
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_max_element<L2, sizeof_less>, char[4]>));
+
+        using L3 = mp_list<char[2], char[4], char[2], char[3], char[1], char[2], char[1]>;
+
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_max_element<L3, sizeof_less>, char[4]>));
+    }
+
+    {
+        using L1 = std::tuple<void>;
+
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_max_element<L1, sizeof_less>, void>));
+
+        using L2 = std::tuple<char[2], char[4], char[3], char[1]>;
+
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_max_element<L2, sizeof_less>, char[4]>));
+
+        using L3 = std::tuple<char[2], char[4], char[2], char[3], char[1], char[2], char[1]>;
+
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_max_element<L3, sizeof_less>, char[4]>));
+    }
+
+    return boost::report_errors();
+}

test/mp_min_element.cpp

@@ -0,0 +1,55 @@
+
+// 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/core/lightweight_test_trait.hpp>
+#include <type_traits>
+#include <tuple>
+
+using boost::mp11::mp_bool;
+
+template<class T, class U> using sizeof_less = mp_bool<(sizeof(T) < sizeof(U))>;
+
+int main()
+{
+    using boost::mp11::mp_list;
+    using boost::mp11::mp_min_element;
+
+    {
+        using L1 = mp_list<void>;
+
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_min_element<L1, sizeof_less>, void>));
+
+        using L2 = mp_list<char[2], char[4], char[3], char[1]>;
+
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_min_element<L2, sizeof_less>, char[1]>));
+
+        using L3 = mp_list<char[2], char[4], char[2], char[3], char[1], char[2], char[1]>;
+
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_min_element<L3, sizeof_less>, char[1]>));
+    }
+
+    {
+        using L1 = std::tuple<void>;
+
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_min_element<L1, sizeof_less>, void>));
+
+        using L2 = std::tuple<char[2], char[4], char[3], char[1]>;
+
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_min_element<L2, sizeof_less>, char[1]>));
+
+        using L3 = std::tuple<char[2], char[4], char[2], char[3], char[1], char[2], char[1]>;
+
+        BOOST_TEST_TRAIT_TRUE((std::is_same<mp_min_element<L3, sizeof_less>, char[1]>));
+    }
+
+    return boost::report_errors();
+}