Add mp_map_update_q

doc/mp11/map.adoc

@@ -55,6 +55,26 @@ replaces the existing element with `T`.
 If the map `M` does not contain an element with a key `mp_first<T>`, inserts it (using `mp_push_back<M, T>`); otherwise,
 replaces the existing element `L<X, Y...>` with `L<X, F<X, Y...>>`.
 
+.Using mp_map_update to count the number of occurences of types in a list
+```
+template<class T, class U> using inc2nd = mp_int<U::value + 1>;
+
+template<class M, class T> using count_types =
+    mp_map_update<M, std::pair<T, mp_int<1>>, inc2nd>;
+
+using L1 = mp_list<float, char, float, float, float, float, char, float>;
+
+using R1 = mp_fold<L1, std::tuple<>, count_types>;
+// std::tuple<std::pair<float, mp_int<6>>, std::pair<char, mp_int<2>>>
+```
+
+## mp_map_update_q<M, T, Q>
+
+    template<class M, class T, class Q> using mp_map_update_q =
+        mp_map_update<M, T, Q::template fn>;
+
+As `mp_map_update`, but takes a quoted metafunction.
+
 ## mp_map_erase<M, K>
 
     template<class M, class K> using mp_map_erase = /*...*/;

include/boost/mp11/map.hpp

@@ -66,6 +66,7 @@ template<class M, class T, template<class...> class F> struct mp_map_update_impl
 } // namespace detail
 
 template<class M, class T, template<class...> class F> using mp_map_update = typename detail::mp_map_update_impl<M, T, F>::type;
+template<class M, class T, class Q> using mp_map_update_q = mp_map_update<M, T, Q::template fn>;
 
 // mp_map_erase<M, K>
 namespace detail

test/Jamfile

@@ -149,6 +149,7 @@ run mp_map_insert.cpp ;
 run mp_map_replace.cpp ;
 run mp_map_erase.cpp ;
 run mp_map_update.cpp ;
+run mp_map_update_q.cpp ;
 run mp_map_keys.cpp ;
 run mp_is_map.cpp ;
 

test/mp_map_update_q.cpp

@@ -0,0 +1,51 @@
+
+// Copyright 2016, 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/map.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>
+
+using boost::mp11::mp_int;
+
+struct Q_inc
+{
+    template<class T, class U> using fn = mp_int<U::value + 1>;
+};
+
+int main()
+{
+    using boost::mp11::mp_map_update_q;
+    using boost::mp11::mp_list;
+
+    using M1 = mp_list<>;
+
+    using M2 = mp_map_update_q<M1, std::pair<char, mp_int<0>>, Q_inc>;
+    BOOST_TEST_TRAIT_TRUE((std::is_same<M2, mp_list<std::pair<char, mp_int<0>>>>));
+
+    using M3 = mp_map_update_q<M2, std::pair<char, mp_int<0>>, Q_inc>;
+    BOOST_TEST_TRAIT_TRUE((std::is_same<M3, mp_list<std::pair<char, mp_int<1>>>>));
+
+    using M4 = mp_map_update_q<M3, std::pair<int, mp_int<0>>, Q_inc>;
+    BOOST_TEST_TRAIT_TRUE((std::is_same<M4, mp_list<std::pair<char, mp_int<1>>, std::pair<int, mp_int<0>>>>));
+
+    using M5 = mp_map_update_q<M4, std::pair<long, mp_int<0>>, Q_inc>;
+    BOOST_TEST_TRAIT_TRUE((std::is_same<M5, mp_list<std::pair<char, mp_int<1>>, std::pair<int, mp_int<0>>, std::pair<long, mp_int<0>>>>));
+
+    using M6 = mp_map_update_q<M5, std::pair<long, mp_int<0>>, Q_inc>;
+    BOOST_TEST_TRAIT_TRUE((std::is_same<M6, mp_list<std::pair<char, mp_int<1>>, std::pair<int, mp_int<0>>, std::pair<long, mp_int<1>>>>));
+
+    using M7 = mp_map_update_q<M6, std::pair<char, mp_int<0>>, Q_inc>;
+    BOOST_TEST_TRAIT_TRUE((std::is_same<M7, mp_list<std::pair<char, mp_int<2>>, std::pair<int, mp_int<0>>, std::pair<long, mp_int<1>>>>));
+
+    return boost::report_errors();
+}