From a0ea1055d29b1b3f54333d28133b9aaff1643bc9 Mon Sep 17 00:00:00 2001
From: Peter Dimov <pdimov@gmail.com>
Date: Sun, 24 May 2020 01:14:46 +0300
Subject: [PATCH] Support up to three tuples in tuple_transform under msvc-12.0

---
 include/boost/mp11/tuple.hpp | 68 +++++++++++++++++-------------------
 test/tuple_transform.cpp     | 20 +----------
 test/tuple_transform_2.cpp   | 12 -------
 3 files changed, 33 insertions(+), 67 deletions(-)

diff --git a/include/boost/mp11/tuple.hpp b/include/boost/mp11/tuple.hpp
index 13c972f..5475211 100644
--- a/include/boost/mp11/tuple.hpp
+++ b/include/boost/mp11/tuple.hpp
@@ -93,40 +93,6 @@ template<class Tp, class F> BOOST_MP11_CONSTEXPR F tuple_for_each( Tp && tp, F &
 namespace detail
 {
 
-template<class... T> BOOST_MP11_CONSTEXPR auto tp_forward( T&&... t ) -> std::tuple<T...>
-{
-    return std::tuple<T...>( std::forward<T>( t )... );
-}
-
-} // namespace detail
-
-#if BOOST_MP11_WORKAROUND( BOOST_MP11_MSVC, < 1900 )
-
-namespace detail
-{
-
-template<class F, class Tp, std::size_t... J>
-BOOST_MP11_CONSTEXPR auto tuple_transform_impl( integer_sequence<std::size_t, J...>, F const& f, Tp&& tp )
-    -> decltype( tp_forward( f( std::get<J>( std::forward<Tp>(tp) ) )... ) )
-{
-    return tp_forward( f( std::get<J>( std::forward<Tp>(tp) ) )... );
-}
-
-} // namespace detail
-
-template<class F, class Tp,
-    class Seq = make_index_sequence<std::tuple_size<typename std::remove_reference<Tp>::type>::value>>
-BOOST_MP11_CONSTEXPR auto tuple_transform( F const& f, Tp&& tp )
-    -> decltype( detail::tuple_transform_impl( Seq(), f, std::forward<Tp>(tp) ) )
-{
-    return detail::tuple_transform_impl( Seq(), f, std::forward<Tp>(tp) );
-}
-
-#else
-
-namespace detail
-{
-
 template<std::size_t J, class... Tp>
 BOOST_MP11_CONSTEXPR auto tp_extract( Tp&&... tp )
     -> decltype( std::forward_as_tuple( std::get<J>( std::forward<Tp>( tp ) )... ) )
@@ -134,6 +100,13 @@ BOOST_MP11_CONSTEXPR auto tp_extract( Tp&&... tp )
     return std::forward_as_tuple( std::get<J>( std::forward<Tp>( tp ) )... );
 }
 
+template<class... T> BOOST_MP11_CONSTEXPR auto tp_forward( T&&... t ) -> std::tuple<T...>
+{
+    return std::tuple<T...>( std::forward<T>( t )... );
+}
+
+#if !BOOST_MP11_WORKAROUND( BOOST_MP11_MSVC, < 1900 )
+
 template<class F, class... Tp, std::size_t... J>
 BOOST_MP11_CONSTEXPR auto tuple_transform_impl( integer_sequence<std::size_t, J...>, F const& f, Tp&&... tp )
     -> decltype( tp_forward( tuple_apply( f, tp_extract<J>( std::forward<Tp>(tp)... ) )... ) )
@@ -141,6 +114,31 @@ BOOST_MP11_CONSTEXPR auto tuple_transform_impl( integer_sequence<std::size_t, J.
     return tp_forward( tuple_apply( f, tp_extract<J>( std::forward<Tp>(tp)... ) )... );
 }
 
+#else
+
+template<class F, class Tp1, std::size_t... J>
+BOOST_MP11_CONSTEXPR auto tuple_transform_impl( integer_sequence<std::size_t, J...>, F const& f, Tp1&& tp1 )
+    -> decltype( tp_forward( f( std::get<J>( std::forward<Tp1>(tp1) ) )... ) )
+{
+    return tp_forward( f( std::get<J>( std::forward<Tp1>(tp1) ) )... );
+}
+
+template<class F, class Tp1, class Tp2, std::size_t... J>
+BOOST_MP11_CONSTEXPR auto tuple_transform_impl( integer_sequence<std::size_t, J...>, F const& f, Tp1&& tp1, Tp2&& tp2 )
+    -> decltype( tp_forward( f( std::get<J>( std::forward<Tp1>(tp1) ), std::get<J>( std::forward<Tp2>(tp2) ) )... ) )
+{
+    return tp_forward( f( std::get<J>( std::forward<Tp1>(tp1) ), std::get<J>( std::forward<Tp2>(tp2) ) )... );
+}
+
+template<class F, class Tp1, class Tp2, class Tp3, std::size_t... J>
+BOOST_MP11_CONSTEXPR auto tuple_transform_impl( integer_sequence<std::size_t, J...>, F const& f, Tp1&& tp1, Tp2&& tp2, Tp3&& tp3 )
+    -> decltype( tp_forward( f( std::get<J>( std::forward<Tp1>(tp1) ), std::get<J>( std::forward<Tp2>(tp2) ), std::get<J>( std::forward<Tp3>(tp3) ) )... ) )
+{
+    return tp_forward( f( std::get<J>( std::forward<Tp1>(tp1) ), std::get<J>( std::forward<Tp2>(tp2) ), std::get<J>( std::forward<Tp3>(tp3) ) )... );
+}
+
+#endif // !BOOST_MP11_WORKAROUND( BOOST_MP11_MSVC, < 1900 )
+
 } // namespace detail
 
 #if BOOST_MP11_WORKAROUND( BOOST_MP11_MSVC, < 1910 )
@@ -167,8 +165,6 @@ BOOST_MP11_CONSTEXPR auto tuple_transform( F const& f, Tp&&... tp )
 
 #endif // BOOST_MP11_WORKAROUND( BOOST_MP11_MSVC, < 1910 )
 
-#endif // BOOST_MP11_WORKAROUND( BOOST_MP11_MSVC, < 1900 )
-
 } // namespace mp11
 } // namespace boost
 
diff --git a/test/tuple_transform.cpp b/test/tuple_transform.cpp
index 2adcaac..22ed0ea 100644
--- a/test/tuple_transform.cpp
+++ b/test/tuple_transform.cpp
@@ -58,8 +58,6 @@ int main()
             BOOST_TEST_EQ( std::get<2>(s).value, 5 );
         }
 
-#if !BOOST_MP11_WORKAROUND( BOOST_MP11_MSVC, < 1900 )
-
         {
             std::tuple<T<5>, T<7>, T<9>> s = tuple_transform( F{}, tp, tp2 );
             BOOST_TEST_EQ( std::get<0>(s).value, 6 );
@@ -75,8 +73,6 @@ int main()
             BOOST_TEST_EQ( std::get<1>(s).value, 8 );
             BOOST_TEST_EQ( std::get<2>(s).value, 10 );
         }
-#endif
-
     }
 
     {
@@ -97,8 +93,6 @@ int main()
             BOOST_TEST_EQ( std::get<2>(s).value, 5 );
         }
 
-#if !BOOST_MP11_WORKAROUND( BOOST_MP11_MSVC, < 1900 )
-
         {
             std::tuple<T<5>, T<7>, T<9>> s = tuple_transform( F{}, tp, tp2 );
             BOOST_TEST_EQ( std::get<0>(s).value, 6 );
@@ -114,8 +108,6 @@ int main()
             BOOST_TEST_EQ( std::get<1>(s).value, 8 );
             BOOST_TEST_EQ( std::get<2>(s).value, 10 );
         }
-#endif
-
     }
 
     {
@@ -134,8 +126,6 @@ int main()
             BOOST_TEST_EQ( std::get<1>(s).value, 4 );
         }
 
-#if !BOOST_MP11_WORKAROUND( BOOST_MP11_MSVC, < 1900 )
-
         {
             std::tuple<T<4>, T<6>> s = tuple_transform( F{}, tp, tp2 );
             BOOST_TEST_EQ( std::get<0>(s).value, 5 );
@@ -149,9 +139,6 @@ int main()
             BOOST_TEST_EQ( std::get<0>(s).value, 5 );
             BOOST_TEST_EQ( std::get<1>(s).value, 7 );
         }
-
-#endif
-
     }
 
     {
@@ -170,8 +157,6 @@ int main()
             BOOST_TEST_EQ( std::get<1>(s).value, 4 );
         }
 
-#if !BOOST_MP11_WORKAROUND( BOOST_MP11_MSVC, < 1900 )
-
         {
             std::tuple<T<4>, T<6>> s = tuple_transform( F{}, tp, tp2 );
             BOOST_TEST_EQ( std::get<0>(s).value, 5 );
@@ -185,10 +170,7 @@ int main()
             BOOST_TEST_EQ( std::get<0>(s).value, 5 );
             BOOST_TEST_EQ( std::get<1>(s).value, 7 );
         }
-
-#endif
-
-	}
+    }
 
     {
         std::tuple<> tp;
diff --git a/test/tuple_transform_2.cpp b/test/tuple_transform_2.cpp
index 4dd89b3..a8c10a9 100644
--- a/test/tuple_transform_2.cpp
+++ b/test/tuple_transform_2.cpp
@@ -63,8 +63,6 @@ int main()
         BOOST_TEST_EQ( std::get<0>( r ), 2 );
     }
 
-#if !BOOST_MP11_WORKAROUND( BOOST_MP11_MSVC, < 1900 )
-
     {
         std::tuple<int> r = tuple_transform( g, ::make_array( 1 ), std::make_tuple( 2 ) );
 
@@ -77,8 +75,6 @@ int main()
         BOOST_TEST_EQ( std::get<0>( r ), 6 );
     }
 
-#endif
-
     //
 
     {
@@ -102,8 +98,6 @@ int main()
         BOOST_TEST_EQ( std::get<1>( r ), 3 );
     }
 
-#if !BOOST_MP11_WORKAROUND( BOOST_MP11_MSVC, < 1900 )
-
     {
         std::tuple<int, int> r = tuple_transform( g, ::make_array( 1, 2 ), std::make_pair( 3, 4 ) );
 
@@ -118,8 +112,6 @@ int main()
         BOOST_TEST_EQ( std::get<1>( r ), 12 );
     }
 
-#endif
-
     //
 
     {
@@ -138,8 +130,6 @@ int main()
         BOOST_TEST_EQ( std::get<2>( r ), 4 );
     }
 
-#if !BOOST_MP11_WORKAROUND( BOOST_MP11_MSVC, < 1900 )
-
     {
         std::tuple<int, int, int> r = tuple_transform( g, ::make_array( 1, 2, 3 ), std::make_tuple( 4, 5, 6 ) );
 
@@ -156,8 +146,6 @@ int main()
         BOOST_TEST_EQ( std::get<2>( r ), 18 );
     }
 
-#endif
-
 #if !BOOST_MP11_WORKAROUND( BOOST_MP11_MSVC, < 1900 )
 
     {