Add mp_not_fn

doc/mp11/utility.adoc

@@ -231,3 +231,20 @@ template<class T> using is_const_and_volatile =
 template<class T> using is_const_and_volatile =
     mp_all<mp_transform<mp_invoke_q, LQ, mp_fill<LQ, T>>>;
 ```
+
+## mp_not_fn<P>
+
+    template<template<class...> class P> struct mp_not_fn
+    {
+        template<class... T> using fn = mp_not<P<T...>>;
+    };
+
+`mp_not_fn<P>` returns a quoted metafunction `Q` such that `Q::fn<T...>` returns `mp_not<P<T...>>`.
+
+That is, it negates the result of `P`.
+
+## mp_not_fn_q<Q>
+
+    template<class Q> using mp_not_fn_q = mp_not_fn<Q::template fn>;
+
+As `mp_not_fn`, but takes a quoted metafunction.

include/boost/mp11/utility.hpp

@@ -212,6 +212,14 @@ template<class Q, class... T> using mp_invoke_q = typename Q::template fn<T...>;
 // old name for mp_invoke_q retained for compatibility, but deprecated
 template<class Q, class... T> using mp_invoke BOOST_MP11_DEPRECATED("please use mp_invoke_q") = mp_invoke_q<Q, T...>;
 
+// mp_not_fn<P>
+template<template<class...> class P> struct mp_not_fn
+{
+    template<class... T> using fn = mp_not< mp_invoke_q<mp_quote<P>, T...> >;
+};
+
+template<class Q> using mp_not_fn_q = mp_not_fn<Q::template fn>;
+
 } // namespace mp11
 } // namespace boost
 

test/Jamfile

@@ -116,6 +116,7 @@ run mp_invoke_q_sf.cpp ;
 run mp_quote_trait.cpp ;
 run mp_cond.cpp ;
 run mp_cond_sf.cpp ;
+run mp_not_fn.cpp ;
 
 # integer_sequence
 run integer_sequence.cpp ;

test/mp_not_fn.cpp

@@ -0,0 +1,36 @@
+
+// Copyright 2019 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/utility.hpp>
+#include <boost/core/lightweight_test_trait.hpp>
+#include <type_traits>
+
+template<class T> using is_const_ = std::is_const<T>;
+
+struct Q_is_const
+{
+    template<class T> using fn = std::is_const<T>;
+};
+
+int main()
+{
+    using boost::mp11::mp_not_fn;
+    using boost::mp11::mp_not_fn_q;
+
+    BOOST_TEST_TRAIT_TRUE((mp_not_fn<std::is_const>::fn<void>));
+    BOOST_TEST_TRAIT_FALSE((mp_not_fn<std::is_const>::fn<void const>));
+
+    BOOST_TEST_TRAIT_TRUE((mp_not_fn<is_const_>::fn<void>));
+    BOOST_TEST_TRAIT_FALSE((mp_not_fn<is_const_>::fn<void const>));
+
+    BOOST_TEST_TRAIT_TRUE((mp_not_fn_q<Q_is_const>::fn<void>));
+    BOOST_TEST_TRAIT_FALSE((mp_not_fn_q<Q_is_const>::fn<void const>));
+
+    return boost::report_errors();
+}