From b52f28c2f3b6fbb5d132d9e122366f19d3598ad9 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Dietmar=20K=C3=BChl?= <dietmar.kuehl@me.com>
Date: Tue, 14 Jan 2025 00:48:51 +0000
Subject: [PATCH] tried to reduce the uses of sender_decompose (#118)

* tried to reduce the uses of sender_decompose

* clang-format
---
 .../beman/execution26/detail/basic_sender.hpp |  7 ++--
 .../beman/execution26/detail/connect_all.hpp  | 39 +++++++++++++++++++
 .../execution26/detail/default_impls.hpp      | 12 +++++-
 .../beman/execution26/detail/product_type.hpp | 14 +++++++
 .../execution26/detail/sender_decompose.hpp   | 23 ++++-------
 tests/beman/execution26/CMakeLists.txt        |  2 +-
 6 files changed, 75 insertions(+), 22 deletions(-)

diff --git a/include/beman/execution26/detail/basic_sender.hpp b/include/beman/execution26/detail/basic_sender.hpp
index ce765f1e..00e4ff33 100644
--- a/include/beman/execution26/detail/basic_sender.hpp
+++ b/include/beman/execution26/detail/basic_sender.hpp
@@ -33,10 +33,9 @@ struct basic_sender : ::beman::execution26::detail::product_type<Tag, Data, Chil
     using indices_for    = ::std::index_sequence_for<Child...>;
 
     auto get_env() const noexcept -> decltype(auto) {
-        auto data{::beman::execution26::detail::get_sender_data(*this)};
-        return ::std::apply(
-            [&data](auto&&... c) { return ::beman::execution26::detail::impls_for<Tag>::get_attrs(data.data, c...); },
-            data.children);
+        auto&& d{this->template get<1>()};
+        return sub_apply<2>(
+            [&d](auto&&... c) { return ::beman::execution26::detail::impls_for<Tag>::get_attrs(d, c...); }, *this);
     }
 
     template <typename Receiver>
diff --git a/include/beman/execution26/detail/connect_all.hpp b/include/beman/execution26/detail/connect_all.hpp
index 057bb6c7..b7a1d3d3 100644
--- a/include/beman/execution26/detail/connect_all.hpp
+++ b/include/beman/execution26/detail/connect_all.hpp
@@ -44,6 +44,33 @@ struct connect_all_t {
                                        ::std::forward<Tuple>(tuple));
     }
 
+    template <::std::size_t Start, typename Fun, typename Tuple, ::std::size_t... I>
+    static auto sub_apply_with_index_helper(::std::index_sequence<I...> seq, Fun&& fun, Tuple&& tuple) noexcept(
+        noexcept(::std::forward<Fun>(fun)(
+            seq, ::beman::execution26::detail::forward_like<Tuple>(tuple.template get<I + Start>())...)))
+        -> decltype(auto) {
+        return ::std::forward<Fun>(fun)(
+            seq, ::beman::execution26::detail::forward_like<Tuple>(tuple.template get<I + Start>())...);
+    }
+    template <::std::size_t Start, typename Fun, typename Tuple>
+        requires requires { ::std::declval<Tuple>().size(); }
+    static auto sub_apply_with_index(Fun&& fun, Tuple&& tuple) noexcept(noexcept(sub_apply_with_index_helper<Start>(
+        ::std::make_index_sequence<::std::tuple_size_v<::std::decay_t<Tuple>> - Start>{},
+        ::std::forward<Fun>(fun),
+        ::std::forward<Tuple>(tuple)))) -> decltype(auto) {
+        return sub_apply_with_index_helper<Start>(
+            ::std::make_index_sequence<::std::tuple_size_v<::std::decay_t<Tuple>> - Start>{},
+            ::std::forward<Fun>(fun),
+            ::std::forward<Tuple>(tuple));
+    }
+    template <::std::size_t Start, typename Fun, typename Tuple>
+        requires(not requires { ::std::declval<Tuple>().size(); })
+    static auto
+    sub_apply_with_index(Fun&& fun,
+                         Tuple&&) noexcept(noexcept(::std::forward<Fun>(fun)(::std::make_index_sequence<0u>{}))) {
+        return ::std::forward<Fun>(fun)(::std::make_index_sequence<0u>{});
+    }
+
     template <typename Sender, typename Receiver>
     struct connect_helper {
         ::beman::execution26::detail::basic_state<Sender, Receiver>* op;
@@ -66,6 +93,18 @@ struct connect_all_t {
 
   public:
     //-dk:TODO is the S parameter deviating from the spec?
+    template <typename Sender, typename S, typename Receiver, ::std::size_t... I>
+        requires requires(Sender&& s) {
+            s.size();
+            s.template get<0>();
+        }
+    auto operator()(::beman::execution26::detail::basic_state<Sender, Receiver>* op,
+                    S&&                                                          sender,
+                    ::std::index_sequence<I...>) const
+        noexcept(noexcept(sub_apply_with_index<2>(connect_helper<Sender, Receiver>{op}, ::std::forward<S>(sender))))
+            -> decltype(auto) {
+        return sub_apply_with_index<2>(connect_helper<Sender, Receiver>{op}, ::std::forward<S>(sender));
+    }
     template <typename Sender, typename S, typename Receiver, ::std::size_t... I>
     auto operator()(::beman::execution26::detail::basic_state<Sender, Receiver>* op,
                     S&&                                                          sender,
diff --git a/include/beman/execution26/detail/default_impls.hpp b/include/beman/execution26/detail/default_impls.hpp
index d4f44bb2..fd84eaf9 100644
--- a/include/beman/execution26/detail/default_impls.hpp
+++ b/include/beman/execution26/detail/default_impls.hpp
@@ -37,10 +37,18 @@ struct default_impls {
     };
     static constexpr auto get_state =
         []<typename Sender, typename Receiver>(Sender&& sender, Receiver& receiver) noexcept -> decltype(auto) {
-        auto&& decompose = ::beman::execution26::detail::get_sender_data(::std::forward<Sender>(sender));
+        auto&& data{[&sender]() -> decltype(auto) {
+            if constexpr (requires {
+                              sender.size();
+                              sender.template get<1>();
+                          })
+                return sender.template get<1>();
+            else
+                return ::beman::execution26::detail::get_sender_data(::std::forward<Sender>(sender)).data;
+        }()};
 
         return ::beman::execution26::detail::allocator_aware_move(
-            ::beman::execution26::detail::forward_like<Sender>(decompose.data), receiver);
+            ::beman::execution26::detail::forward_like<Sender>(data), receiver);
     };
     static constexpr auto start = [](auto&, auto&, auto&... ops) noexcept -> void {
         (::beman::execution26::start(ops), ...);
diff --git a/include/beman/execution26/detail/product_type.hpp b/include/beman/execution26/detail/product_type.hpp
index b309f95c..1c43e8e8 100644
--- a/include/beman/execution26/detail/product_type.hpp
+++ b/include/beman/execution26/detail/product_type.hpp
@@ -112,6 +112,20 @@ template <typename... T>
 constexpr auto is_product_type(const ::beman::execution26::detail::product_type<T...>&) -> ::std::true_type {
     return {};
 }
+
+template <::std::size_t Start, typename Fun, typename Tuple, ::std::size_t... I>
+constexpr auto sub_apply_helper(Fun&& fun, Tuple&& tuple, ::std::index_sequence<I...>) -> decltype(auto) {
+    return ::std::forward<Fun>(fun)(::std::forward<Tuple>(tuple).template get<I + Start>()...);
+}
+
+template <::std::size_t Start, typename Fun, typename Tuple>
+constexpr auto sub_apply(Fun&& fun, Tuple&& tuple) -> decltype(auto) {
+    static constexpr ::std::size_t TSize{::std::tuple_size_v<::std::remove_cvref_t<Tuple>>};
+    static_assert(Start <= TSize);
+    return sub_apply_helper<Start>(
+        ::std::forward<Fun>(fun), ::std::forward<Tuple>(tuple), ::std::make_index_sequence<TSize - Start>());
+}
+
 } // namespace beman::execution26::detail
 
 namespace std {
diff --git a/include/beman/execution26/detail/sender_decompose.hpp b/include/beman/execution26/detail/sender_decompose.hpp
index d8915f54..24d23d45 100644
--- a/include/beman/execution26/detail/sender_decompose.hpp
+++ b/include/beman/execution26/detail/sender_decompose.hpp
@@ -33,6 +33,8 @@ struct sender_data {
     Data&    data;
     Children children;
 };
+template <typename Tag, typename Data, typename Children>
+sender_data(Tag&&, Data&, Children&&) -> sender_data<Tag, Data, Children>;
 
 template <typename Sender>
 auto get_sender_data(Sender&& sender) {
@@ -49,33 +51,24 @@ auto get_sender_data(Sender&& sender) {
                       sender.size();
                   })
         return [&sender]<::std::size_t... I>(::std::index_sequence<I...>) {
-            return ::beman::execution26::detail::sender_data<decltype(sender.template get<0>()),
-                                                             decltype(sender.template get<1>()),
-                                                             decltype(::std::tie(sender.template get<2 + I>()...))>{
+            return ::beman::execution26::detail::sender_data{
                 sender.template get<0>(), sender.template get<1>(), ::std::tie(sender.template get<2 + I>()...)};
         }(::std::make_index_sequence<::std::decay_t<decltype(sender)>::size() - 2u>{});
     else if constexpr (requires { sender_type{at, at, at, at, at, at}; }) {
         auto&& [tag, data, c0, c1, c2, c3] = sender;
-        return ::beman::execution26::detail::
-            sender_data<decltype(tag), decltype(data), decltype(::std::tie(c0, c1, c2, c3))>{
-                tag, data, ::std::tie(c0, c1, c2, c3)};
+        return ::beman::execution26::detail::sender_data{tag, data, ::std::tie(c0, c1, c2, c3)};
     } else if constexpr (requires { sender_type{at, at, at, at, at}; }) {
         auto&& [tag, data, c0, c1, c2] = sender;
-        return ::beman::execution26::detail::
-            sender_data<decltype(tag), decltype(data), decltype(::std::tie(c0, c1, c2))>{
-                tag, data, ::std::tie(c0, c1, c2)};
+        return ::beman::execution26::detail::sender_data{tag, data, ::std::tie(c0, c1, c2)};
     } else if constexpr (requires { sender_type{at, at, at, at}; }) {
         auto&& [tag, data, c0, c1] = sender;
-        return ::beman::execution26::detail::sender_data<decltype(tag), decltype(data), decltype(::std::tie(c0, c1))>{
-            tag, data, ::std::tie(c0, c1)};
+        return ::beman::execution26::detail::sender_data{tag, data, ::std::tie(c0, c1)};
     } else if constexpr (requires { sender_type{at, at, at}; }) {
         auto&& [tag, data, c0] = sender;
-        return ::beman::execution26::detail::sender_data<decltype(tag), decltype(data), decltype(::std::tie(c0))>{
-            tag, data, ::std::tie(c0)};
+        return ::beman::execution26::detail::sender_data{tag, data, ::std::tie(c0)};
     } else if constexpr (requires { sender_type{at, at}; }) {
         auto&& [tag, data] = sender;
-        return ::beman::execution26::detail::sender_data<decltype(tag), decltype(data), ::std::tuple<>>{
-            tag, data, ::std::tuple<>()};
+        return ::beman::execution26::detail::sender_data{tag, data, ::std::tuple<>()};
     } else {
         return ::beman::execution26::detail::sender_meta<void, void, void>{};
     }
diff --git a/tests/beman/execution26/CMakeLists.txt b/tests/beman/execution26/CMakeLists.txt
index b9130f6e..56a8d1c8 100644
--- a/tests/beman/execution26/CMakeLists.txt
+++ b/tests/beman/execution26/CMakeLists.txt
@@ -129,7 +129,7 @@ foreach(test ${execution_tests})
   add_test(NAME ${TEST_EXE} COMMAND $<TARGET_FILE:${TEST_EXE}>)
 endforeach()
 
-if(NOT PROJECT_IS_TOP_LEVEL)
+if(ROJECT_IS_TOP_LEVEL)
   # test if the targets are findable from the build directory
   # cmake-format: off
   add_test(NAME find-package-test