Add mp_compose

include/boost/mp11/utility.hpp

@@ -1,7 +1,7 @@
 #ifndef BOOST_MP11_UTILITY_HPP_INCLUDED
 #define BOOST_MP11_UTILITY_HPP_INCLUDED
 
-// Copyright 2015, 2017, 2019 Peter Dimov.
+// Copyright 2015-2020 Peter Dimov.
 //
 // Distributed under the Boost Software License, Version 1.0.
 //
@@ -9,6 +9,8 @@
 // http://www.boost.org/LICENSE_1_0.txt
 
 #include <boost/mp11/integral.hpp>
+#include <boost/mp11/detail/mp_list.hpp>
+#include <boost/mp11/detail/mp_fold.hpp>
 #include <boost/mp11/detail/config.hpp>
 
 namespace boost
@@ -230,6 +232,32 @@ template<template<class...> class P> struct mp_not_fn
 
 template<class Q> using mp_not_fn_q = mp_not_fn<Q::template fn>;
 
+// mp_compose
+namespace detail
+{
+
+template<class T, class Q> using mp_reverse_invoke_q = mp_invoke_q<Q, T>;
+
+} // namespace detail
+
+#if !BOOST_MP11_WORKAROUND( BOOST_MP11_MSVC, < 1900 )
+
+template<template<class...> class... F> struct mp_compose
+{
+    template<class T> using fn = mp_fold<mp_list<mp_quote<F>...>, T, detail::mp_reverse_invoke_q>;
+};
+
+template<class... Q> using mp_compose_q = mp_compose<Q::template fn...>;
+
+#else
+
+template<class... Q> struct mp_compose_q
+{
+    template<class T> using fn = mp_fold<mp_list<Q...>, T, detail::mp_reverse_invoke_q>;
+};
+
+#endif
+
 } // namespace mp11
 } // namespace boost
 

test/Jamfile

@@ -141,6 +141,7 @@ run mp_cond_sf.cpp ;
 run mp_not_fn.cpp ;
 run mp_eval_if_not.cpp ;
 run mp_eval_or.cpp ;
+run mp_compose.cpp ;
 
 # integer_sequence
 run integer_sequence.cpp ;

test/mp_compose.cpp

@@ -0,0 +1,59 @@
+
+// Copyright 2017, 2020 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+
+#include <boost/mp11/utility.hpp>
+#include <boost/core/lightweight_test_trait.hpp>
+
+template<class T> struct F1 {};
+template<class T> struct F2 {};
+template<class T> struct F3 {};
+
+template<class T> using G1 = F1<T>;
+template<class T> using G2 = F2<T>;
+template<class T> using G3 = F3<T>;
+
+int main()
+{
+    using namespace boost::mp11;
+
+#if !BOOST_MP11_WORKAROUND( BOOST_MP11_MSVC, < 1900 )
+
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_compose<>::fn<void>, void>));
+
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_compose<F1>::fn<void>, F1<void>>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_compose<G1>::fn<void>, F1<void>>));
+
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_compose<F1, F2>::fn<void>, F2<F1<void>>>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_compose<G1, G2>::fn<void>, F2<F1<void>>>));
+
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_compose<F1, F2, F3>::fn<void>, F3<F2<F1<void>>>>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_compose<G1, G2, G3>::fn<void>, F3<F2<F1<void>>>>));
+
+#endif
+
+    using QF1 = mp_quote<F1>;
+    using QF2 = mp_quote<F2>;
+    using QF3 = mp_quote<F3>;
+
+    using QG1 = mp_quote<G1>;
+    using QG2 = mp_quote<G2>;
+    using QG3 = mp_quote<G3>;
+
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_compose_q<>::fn<void>, void>));
+
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_compose_q<QF1>::fn<void>, F1<void>>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_compose_q<QG1>::fn<void>, F1<void>>));
+
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_compose_q<QF1, QF2>::fn<void>, F2<F1<void>>>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_compose_q<QG1, QG2>::fn<void>, F2<F1<void>>>));
+
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_compose_q<QF1, QF2, QF3>::fn<void>, F3<F2<F1<void>>>>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_compose_q<QG1, QG2, QG3>::fn<void>, F3<F2<F1<void>>>>));
+
+    //
+
+    return boost::report_errors();
+}