From dcf0d7ebdfb6607e98ee44f52655a23b12476acc Mon Sep 17 00:00:00 2001
From: Peter Dimov <pdimov@gmail.com>
Date: Sat, 23 May 2020 19:16:07 +0300
Subject: [PATCH] Squash-merge PR #50

---
 doc/mp11/changelog.adoc      |   1 +
 doc/mp11/tuple.adoc          |  12 +++
 include/boost/mp11/tuple.hpp |  77 ++++++++++++++
 test/Jamfile                 |   2 +
 test/tuple_transform.cpp     | 190 +++++++++++++++++++++++++++++++++++
 test/tuple_transform_cx.cpp  |  75 ++++++++++++++
 6 files changed, 357 insertions(+)
 create mode 100644 test/tuple_transform.cpp
 create mode 100644 test/tuple_transform_cx.cpp

diff --git a/doc/mp11/changelog.adoc b/doc/mp11/changelog.adoc
index 7d707f8..94822fa 100644
--- a/doc/mp11/changelog.adoc
+++ b/doc/mp11/changelog.adoc
@@ -13,6 +13,7 @@ http://www.boost.org/LICENSE_1_0.txt
 ## Changes in 1.74.0
 
 * Improve compilation performance of `mp_with_index<N>` for large `N`
+* Added `tuple_transform` (contributed by Hans Dembinski)
 
 ## Changes in 1.73.0
 
diff --git a/doc/mp11/tuple.adoc b/doc/mp11/tuple.adoc
index 46baab3..25da1fd 100644
--- a/doc/mp11/tuple.adoc
+++ b/doc/mp11/tuple.adoc
@@ -36,3 +36,15 @@ The name of the function doesn't match the {cpp}17 one to avoid ambiguities when
 expression `f(std::get<J>(std::forward<Tp>(tp)))` for `J` in 0..`N-1`, where `N` is `std::tuple_size<typename std::remove_reference<Tp>::type>::value`.
 
 Returns `std::forward<F>(f)`.
+
+## tuple_transform(f, tp)
+
+    template<class F, class... Tps> constexpr /*...*/ tuple_transform(F const& f, Tps const&... tps);
+
+`tuple_transform(f, tps...)` accepts a function object `f` followed by one or more tuples of equal length
+(`std::pair` is also accepted). The callable `f` must accept as many arguments as there are tuples. The
+function object is called with the first elements of each tuple, then with the second element of each tuple,
+and so on, by evaluating the expression `f(std::get<J>(tps)...)` for `J` in 0..`N-1`, where `N` is
+`std::tuple_size<Tp>::value` for the first tuple `Tp`. The results are returned as a `Tp<Ts...>` with `Ts...`
+deduced from the return values of `f`. Warning: The order in which the elements of the tuples are processed
+is undefined. Calling `f` should not have side-effects.
diff --git a/include/boost/mp11/tuple.hpp b/include/boost/mp11/tuple.hpp
index c65be1b..872f70f 100644
--- a/include/boost/mp11/tuple.hpp
+++ b/include/boost/mp11/tuple.hpp
@@ -86,6 +86,83 @@ template<class Tp, class F> BOOST_MP11_CONSTEXPR F tuple_for_each( Tp && tp, F &
     return detail::tuple_for_each_impl( std::forward<Tp>(tp), seq(), std::forward<F>(f) );
 }
 
+// tuple_transform
+namespace detail
+{
+
+template <class Tp, class F, class... Tps>
+struct tuple_transform_caller {
+    F const& f_;
+    std::tuple<Tp const&, Tps const&...> const tps_;
+
+    BOOST_MP11_CONSTEXPR tuple_transform_caller( Tp const& tp, F const& f, Tps const&... tps )
+        : f_{f}, tps_{tp, tps...} {}
+
+    template <std::size_t J, std::size_t... I>
+    BOOST_MP11_CONSTEXPR auto operator()(
+        std::integral_constant<std::size_t, J>,
+        integer_sequence<std::size_t, I...>) const
+        -> decltype(f_(std::get<J>(std::get<I>(tps_))...))
+    {
+        return f_(std::get<J>(std::get<I>(tps_))...);
+    }
+};
+
+template <class Tp, class F>
+struct tuple_transform_caller<Tp, F> {
+    F const& f_;
+    Tp const& tp_;
+
+    BOOST_MP11_CONSTEXPR tuple_transform_caller( Tp const& tp, F const& f )
+        : f_{f}, tp_{tp} {}
+
+    template <std::size_t J>
+    BOOST_MP11_CONSTEXPR auto operator()(
+        std::integral_constant<std::size_t, J>,
+        integer_sequence<std::size_t, 0>
+    ) const
+        -> decltype(f_(std::get<J>(tp_)))
+    {
+        return f_(std::get<J>(tp_));
+    }
+};
+
+template<
+    template <class...> class Tp,
+    class... Ts,
+    class... Us,
+    std::size_t... J,
+    class Seq = make_index_sequence<sizeof...(Us)>, // tuple sequence
+    class R = Tp<decltype(std::declval<tuple_transform_caller<Tp<Ts...>, Us...>>()(
+        std::integral_constant<std::size_t, J>{}, Seq{}
+    ))...>
+>
+BOOST_MP11_CONSTEXPR R tuple_transform_impl(
+    tuple_transform_caller<Tp<Ts...>, Us...> c,
+    integer_sequence<std::size_t, J...>)
+{
+    return R( c(std::integral_constant<std::size_t, J>{}, Seq{})... );
+}
+
+} // namespace detail
+
+// warning: evaluation order is undefined
+template<
+  class F,
+  class Tp,
+  class... Tps,
+  class Seq = make_index_sequence<std::tuple_size<Tp>::value> // element sequence
+>
+BOOST_MP11_CONSTEXPR auto tuple_transform( F const& f, Tp const& tp, Tps const&... tps )
+  -> decltype(detail::tuple_transform_impl(
+        std::declval<detail::tuple_transform_caller<Tp, F, Tps...>>(), Seq{}
+    ))
+{
+    return detail::tuple_transform_impl(
+        detail::tuple_transform_caller<Tp, F, Tps...>{ tp, f, tps... }, Seq{}
+    );
+}
+
 } // namespace mp11
 } // namespace boost
 
diff --git a/test/Jamfile b/test/Jamfile
index dc2d062..15fef4c 100644
--- a/test/Jamfile
+++ b/test/Jamfile
@@ -156,6 +156,8 @@ run tuple_apply.cpp ;
 compile tuple_apply_cx.cpp ;
 run construct_from_tuple.cpp ;
 compile construct_from_tuple_cx.cpp ;
+run tuple_transform.cpp ;
+compile tuple_transform_cx.cpp ;
 
 # set
 run mp_set_contains.cpp ;
diff --git a/test/tuple_transform.cpp b/test/tuple_transform.cpp
new file mode 100644
index 0000000..d7d0b79
--- /dev/null
+++ b/test/tuple_transform.cpp
@@ -0,0 +1,190 @@
+
+// Copyright 2020 Hans Dembinski.
+//
+// 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/tuple.hpp>
+#include <boost/core/lightweight_test.hpp>
+#include <boost/core/lightweight_test_trait.hpp>
+#include <tuple>
+#include <utility>
+#include <iosfwd>
+
+// family of test types with state
+template <int N>
+struct T {
+    int value;
+    T() : value{N} {};
+    explicit T(int n) : value{n} {}
+};
+
+template <int N>
+std::ostream& operator<<( std::ostream& os, T<N> const& t )
+{
+    os << t.value;
+    return os;
+}
+
+// test function changes type and value
+struct F {
+    template<int N, int M=1> T<N+M> operator()( T<N> a, T<M> b={} ) const
+    {
+        return T<N+M>{a.value + b.value + 1};
+    }
+};
+
+int main()
+{
+    using boost::mp11::tuple_transform;
+
+    {
+        std::tuple<T<1>, T<2>, T<3>> tp;
+        std::tuple<T<4>, T<5>, T<6>> tp2;
+
+        {
+            std::tuple<T<2>, T<3>, T<4>> s = tuple_transform( F{}, tp );
+            BOOST_TEST_EQ( std::get<0>(s).value, 3 );
+            BOOST_TEST_EQ( std::get<1>(s).value, 4 );
+            BOOST_TEST_EQ( std::get<2>(s).value, 5 );
+        }
+
+        {
+            std::tuple<T<2>, T<3>, T<4>> s = tuple_transform( F{}, std::move(tp) );
+            BOOST_TEST_EQ( std::get<0>(s).value, 3 );
+            BOOST_TEST_EQ( std::get<1>(s).value, 4 );
+            BOOST_TEST_EQ( std::get<2>(s).value, 5 );
+        }
+
+        {
+            std::tuple<T<5>, T<7>, T<9>> s = tuple_transform( F{}, tp, tp2 );
+            BOOST_TEST_EQ( std::get<0>(s).value, 6 );
+            BOOST_TEST_EQ( std::get<1>(s).value, 8 );
+            BOOST_TEST_EQ( std::get<2>(s).value, 10 );
+        }
+
+        {
+            std::tuple<T<5>, T<7>, T<9>> s = tuple_transform(
+                F{}, std::move(tp), std::move(tp2)
+            );
+            BOOST_TEST_EQ( std::get<0>(s).value, 6 );
+            BOOST_TEST_EQ( std::get<1>(s).value, 8 );
+            BOOST_TEST_EQ( std::get<2>(s).value, 10 );
+        }
+    }
+
+    {
+        std::tuple<T<1>, T<2>, T<3>> const tp;
+        std::tuple<T<4>, T<5>, T<6>> const tp2;
+
+        {
+            std::tuple<T<2>, T<3>, T<4>> s = tuple_transform( F{}, tp );
+            BOOST_TEST_EQ( std::get<0>(s).value, 3 );
+            BOOST_TEST_EQ( std::get<1>(s).value, 4 );
+            BOOST_TEST_EQ( std::get<2>(s).value, 5 );
+        }
+
+        {
+            std::tuple<T<2>, T<3>, T<4>> s = tuple_transform( F{}, std::move(tp) );
+            BOOST_TEST_EQ( std::get<0>(s).value, 3 );
+            BOOST_TEST_EQ( std::get<1>(s).value, 4 );
+            BOOST_TEST_EQ( std::get<2>(s).value, 5 );
+        }
+
+        {
+            std::tuple<T<5>, T<7>, T<9>> s = tuple_transform( F{}, tp, tp2 );
+            BOOST_TEST_EQ( std::get<0>(s).value, 6 );
+            BOOST_TEST_EQ( std::get<1>(s).value, 8 );
+            BOOST_TEST_EQ( std::get<2>(s).value, 10 );
+        }
+
+        {
+            std::tuple<T<5>, T<7>, T<9>> s = tuple_transform(
+                F{}, std::move(tp), std::move(tp2)
+            );
+            BOOST_TEST_EQ( std::get<0>(s).value, 6 );
+            BOOST_TEST_EQ( std::get<1>(s).value, 8 );
+            BOOST_TEST_EQ( std::get<2>(s).value, 10 );
+        }
+    }
+
+    {
+        std::pair<T<1>, T<2>> tp;
+        std::pair<T<3>, T<4>> tp2;
+
+        {
+            std::pair<T<2>, T<3>> s = tuple_transform( F{}, tp );
+            BOOST_TEST_EQ( std::get<0>(s).value, 3 );
+            BOOST_TEST_EQ( std::get<1>(s).value, 4 );
+        }
+
+        {
+            std::pair<T<2>, T<3>> s = tuple_transform( F{}, std::move(tp) );
+            BOOST_TEST_EQ( std::get<0>(s).value, 3 );
+            BOOST_TEST_EQ( std::get<1>(s).value, 4 );
+        }
+
+        {
+            std::pair<T<4>, T<6>> s = tuple_transform( F{}, tp, tp2 );
+            BOOST_TEST_EQ( std::get<0>(s).value, 5 );
+            BOOST_TEST_EQ( std::get<1>(s).value, 7 );
+        }
+
+        {
+            std::pair<T<4>, T<6>> s = tuple_transform(
+                F{}, std::move(tp), std::move(tp2)
+            );
+            BOOST_TEST_EQ( std::get<0>(s).value, 5 );
+            BOOST_TEST_EQ( std::get<1>(s).value, 7 );
+        }
+    }
+
+    {
+        std::pair<T<1>, T<2>> const tp;
+        std::pair<T<3>, T<4>> const tp2;
+
+        {
+            std::pair<T<2>, T<3>> s = tuple_transform( F{}, tp );
+            BOOST_TEST_EQ( std::get<0>(s).value, 3 );
+            BOOST_TEST_EQ( std::get<1>(s).value, 4 );
+        }
+
+        {
+            std::pair<T<2>, T<3>> s = tuple_transform( F{}, std::move(tp) );
+            BOOST_TEST_EQ( std::get<0>(s).value, 3 );
+            BOOST_TEST_EQ( std::get<1>(s).value, 4 );
+        }
+
+        {
+            std::pair<T<4>, T<6>> s = tuple_transform( F{}, tp, tp2 );
+            BOOST_TEST_EQ( std::get<0>(s).value, 5 );
+            BOOST_TEST_EQ( std::get<1>(s).value, 7 );
+        }
+
+        {
+            std::pair<T<4>, T<6>> s = tuple_transform(
+                F{}, std::move(tp), std::move(tp2)
+            );
+            BOOST_TEST_EQ( std::get<0>(s).value, 5 );
+            BOOST_TEST_EQ( std::get<1>(s).value, 7 );
+        }
+    }
+
+    {
+        std::tuple<> tp;
+
+        {
+            auto s = tuple_transform( F{}, tp );
+            BOOST_TEST_TRAIT_TRUE((std::is_same<decltype(s), std::tuple<>>));
+        }
+
+        {
+            auto s = tuple_transform( F{}, std::move(tp) );
+            BOOST_TEST_TRAIT_TRUE((std::is_same<decltype(s), std::tuple<>>));
+        }
+    }
+
+    return boost::report_errors();
+}
diff --git a/test/tuple_transform_cx.cpp b/test/tuple_transform_cx.cpp
new file mode 100644
index 0000000..2b07d52
--- /dev/null
+++ b/test/tuple_transform_cx.cpp
@@ -0,0 +1,75 @@
+
+// Copyright 2020 Hans Dembinski.
+//
+// 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/tuple.hpp>
+#include <boost/mp11/detail/config.hpp>
+
+// Technically std::tuple isn't constexpr enabled in C++11, but it works with libstdc++
+
+#if defined( BOOST_MP11_NO_CONSTEXPR ) || ( !defined( __GLIBCXX__ ) && __cplusplus < 201400L )
+
+int main() {}
+
+#else
+
+#include <tuple>
+#include <type_traits>
+
+// family of test types with state
+template <int N>
+struct T {
+    int value;
+    constexpr T() : value{N} {};
+    constexpr explicit T(int n) : value{n} {}
+};
+
+struct F
+{
+    template<int N, int M=1> constexpr T<N+M> operator()( T<N> a, T<M> b={} ) const
+    {
+        return T<N+M>{a.value + b.value + 1};
+    }
+};
+
+int main()
+{
+    {
+        constexpr std::tuple<T<1>, T<2>> tp;
+        constexpr std::tuple<T<3>, T<4>> tp2;
+
+        {
+            constexpr std::tuple<T<2>, T<3>> r = boost::mp11::tuple_transform(
+                F{}, tp
+            );
+            static_assert(std::get<0>(r).value == 3, "get<0>(r).value == 3" );
+            static_assert(std::get<1>(r).value == 4, "get<1>(r).value == 4" );
+        }
+
+        {
+            constexpr std::tuple<T<4>, T<6>> r = boost::mp11::tuple_transform(
+                F{}, tp, tp2
+            );
+            static_assert(std::get<0>(r).value == 5, "get<0>(r).value == 5" );
+            static_assert(std::get<1>(r).value == 7, "get<1>(r).value == 7" );
+        }
+    }
+
+#if defined( __clang_major__ ) && __clang_major__ == 3 && __clang_minor__ < 9
+// "error: default initialization of an object of const type 'const std::tuple<>' without a user-provided default constructor"
+#else
+
+    {
+        constexpr std::tuple<> tp;
+        constexpr std::tuple<> r = boost::mp11::tuple_transform( F{}, tp );
+        (void)r;
+    }
+
+#endif
+}
+
+#endif