From c418e38a27d10132c2113109d90e47e2422267b9 Mon Sep 17 00:00:00 2001
From: Maikel Nadolski <maikel.nadolski@gmail.com>
Date: Wed, 8 Jan 2025 14:39:09 +0100
Subject: [PATCH 1/5] WIP: initial implementation of D3206R0

---
 .../beman/execution26/detail/basic_sender.hpp | 35 +++++++---
 .../detail/completion_behaviour.hpp           | 13 ++++
 .../execution26/detail/default_impls.hpp      |  4 ++
 .../detail/get_completion_behaviour.hpp       | 68 +++++++++++++++++++
 include/beman/execution26/detail/just.hpp     |  8 ++-
 src/beman/execution26/CMakeLists.txt          |  2 +
 tests/beman/execution26/CMakeLists.txt        |  1 +
 .../exec-get-completion-behaviour.test.cpp    | 53 +++++++++++++++
 8 files changed, 174 insertions(+), 10 deletions(-)
 create mode 100644 include/beman/execution26/detail/completion_behaviour.hpp
 create mode 100644 include/beman/execution26/detail/get_completion_behaviour.hpp
 create mode 100644 tests/beman/execution26/exec-get-completion-behaviour.test.cpp

diff --git a/include/beman/execution26/detail/basic_sender.hpp b/include/beman/execution26/detail/basic_sender.hpp
index ce765f1e..ae7a2e65 100644
--- a/include/beman/execution26/detail/basic_sender.hpp
+++ b/include/beman/execution26/detail/basic_sender.hpp
@@ -39,16 +39,29 @@ struct basic_sender : ::beman::execution26::detail::product_type<Tag, Data, Chil
             data.children);
     }
 
+    template <class Self, class Env>
+    constexpr auto get_completion_behaviour(this Self&& self, Env&& env) noexcept -> decltype(auto) {
+        auto data{::beman::execution26::detail::get_sender_data(self)};
+        return ::std::apply(
+            [&data, &env](auto&&... cs) {
+                return ::beman::execution26::detail::impls_for<Tag>::get_completion_behaviour(
+                    ::std::forward<Env>(env),
+                    ::beman::execution26::detail::forward_like<Self>(data.data),
+                    ::beman::execution26::detail::forward_like<Self>(cs)...);
+            },
+            ::beman::execution26::detail::forward_like<Self>(data.children));
+    }
+
     template <typename Receiver>
-        requires(not::beman::execution26::receiver<Receiver>)
+        requires(not ::beman::execution26::receiver<Receiver>)
     auto connect(Receiver receiver) = BEMAN_EXECUTION26_DELETE("the passed receiver doesn't model receiver");
 
   private:
 #if __cpp_explicit_this_parameter < 302110L //-dk:TODO need to figure out how to use explicit this with forwarding
     template <::beman::execution26::receiver Receiver>
     auto connect(Receiver receiver) & noexcept(
-        noexcept(::beman::execution26::detail::basic_operation<basic_sender&, Receiver>{*this, ::std::move(receiver)}))
-        -> ::beman::execution26::detail::basic_operation<basic_sender&, Receiver> {
+        noexcept(::beman::execution26::detail::basic_operation<basic_sender&, Receiver>{
+            *this, ::std::move(receiver)})) -> ::beman::execution26::detail::basic_operation<basic_sender&, Receiver> {
         return {*this, ::std::move(receiver)};
     }
     template <::beman::execution26::receiver Receiver>
@@ -59,9 +72,9 @@ struct basic_sender : ::beman::execution26::detail::product_type<Tag, Data, Chil
     }
     template <::beman::execution26::receiver Receiver>
     auto connect(Receiver receiver) && noexcept(
-        noexcept(::beman::execution26::detail::basic_operation<basic_sender, Receiver>{::std::move(*this),
-                                                                                       ::std::move(receiver)}))
-        -> ::beman::execution26::detail::basic_operation<basic_sender, Receiver> {
+        noexcept(::beman::execution26::detail::basic_operation<basic_sender, Receiver>{
+            ::std::move(*this),
+            ::std::move(receiver)})) -> ::beman::execution26::detail::basic_operation<basic_sender, Receiver> {
         return {::std::move(*this), ::std::move(receiver)};
     }
 #else
@@ -69,8 +82,8 @@ struct basic_sender : ::beman::execution26::detail::product_type<Tag, Data, Chil
     auto
     connect(this Self&& self,
             Receiver receiver) noexcept(noexcept(::beman::execution26::detail::basic_operation<basic_sender, Receiver>{
-        ::std::forward<Self>(self), ::std::move(receiver)}))
-        -> ::beman::execution26::detail::basic_operation<Self, Receiver> {
+        ::std::forward<Self>(self),
+        ::std::move(receiver)})) -> ::beman::execution26::detail::basic_operation<Self, Receiver> {
         return {::std::forward<Self>(self), ::std::move(receiver)};
     }
 #endif
@@ -101,6 +114,12 @@ struct basic_sender : ::beman::execution26::detail::product_type<Tag, Data, Chil
         -> ::beman::execution26::detail::completion_signatures_for<Self, Env> {
         return {};
     }
+
+    template <::beman::execution26::detail::decays_to<basic_sender> Self, typename Env>
+    auto get_completion_behaviour(this Self&&, Env&&) noexcept
+        -> ::beman::execution26::detail::completion_signatures_for<Self, Env> {
+        return {};
+    }
 #endif
 };
 } // namespace beman::execution26::detail
diff --git a/include/beman/execution26/detail/completion_behaviour.hpp b/include/beman/execution26/detail/completion_behaviour.hpp
new file mode 100644
index 00000000..3601caf1
--- /dev/null
+++ b/include/beman/execution26/detail/completion_behaviour.hpp
@@ -0,0 +1,13 @@
+// include/beman/execution26/detail/completion_behaviour.hpp          -*-C++-*-
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+#ifndef INCLUDED_BEMAN_EXECUTION26_DETAIL_COMPLETION_BEHAVIOUR
+#define INCLUDED_BEMAN_EXECUTION26_DETAIL_COMPLETION_BEHAVIOUR
+
+#include <cstdint>
+
+namespace beman::execution26 {
+enum class completion_behaviour : std::uint8_t { inline_completion, synchronous, asynchronous, unknown };
+} // namespace beman::execution26
+
+#endif
diff --git a/include/beman/execution26/detail/default_impls.hpp b/include/beman/execution26/detail/default_impls.hpp
index d4f44bb2..f521d03d 100644
--- a/include/beman/execution26/detail/default_impls.hpp
+++ b/include/beman/execution26/detail/default_impls.hpp
@@ -52,6 +52,10 @@ struct default_impls {
         static_assert(Index::value == 0);
         Tag()(::std::move(receiver), ::std::forward<Args>(args)...);
     };
+    static constexpr auto get_completion_behaviour =
+        [](const auto& /* env */, const auto& /* data */, const auto&... /* children */) noexcept {
+            return ::beman::execution26::completion_behaviour::unknown;
+        };
 };
 } // namespace beman::execution26::detail
 
diff --git a/include/beman/execution26/detail/get_completion_behaviour.hpp b/include/beman/execution26/detail/get_completion_behaviour.hpp
new file mode 100644
index 00000000..bd2e4b53
--- /dev/null
+++ b/include/beman/execution26/detail/get_completion_behaviour.hpp
@@ -0,0 +1,68 @@
+// include/beman/execution26/detail/get_completion_behaviour.hpp      -*-C++-*-
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+#ifndef INCLUDED_BEMAN_EXECUTION26_DETAIL_GET_COMPLETION_BEHAVIOUR
+#define INCLUDED_BEMAN_EXECUTION26_DETAIL_GET_COMPLETION_BEHAVIOUR
+
+#include <beman/execution26/detail/completion_behaviour.hpp>
+#include <beman/execution26/detail/forward_like.hpp>
+#include <beman/execution26/detail/is_awaitable.hpp>
+#include <beman/execution26/detail/get_domain_late.hpp>
+#include <beman/execution26/detail/transform_sender.hpp>
+
+#include <type_traits>
+
+namespace beman::execution26 {
+
+struct get_completion_behaviour_t {
+    template <class Sender>
+    constexpr auto operator()(Sender&& sender) const noexcept {
+        if constexpr (requires { typename ::std::remove_cvref_t<Sender>::completion_behaviour; }) {
+            return typename ::std::remove_cvref_t<Sender>::completion_behaviour{};
+        } else if constexpr (requires { ::std::forward<Sender>(sender).get_completion_behaviour(); }) {
+            return ::std::forward<Sender>(sender).get_completion_behaviour();
+        } else if constexpr (::beman::execution26::detail::is_awaitable<
+                                 ::std::remove_cvref_t<Sender>,
+                                 ::beman::execution26::detail::env_promise<::beman::execution26::empty_env>>) {
+            return sender.await_ready() ? ::beman::execution26::completion_behaviour::inline_completion
+                                        : ::beman::execution26::completion_behaviour::unknown;
+        } else {
+            return ::beman::execution26::completion_behaviour::unknown;
+        }
+    }
+
+    template <class Sender, class Env>
+    constexpr auto operator()(Sender&& sender, Env&& env) const noexcept {
+        auto new_sender{[](auto&& sndr, auto&& e) -> decltype(auto) {
+            auto domain{::beman::execution26::detail::get_domain_late(sndr, e)};
+            return ::beman::execution26::transform_sender(
+                domain, ::std::forward<Sender>(sndr), ::std::forward<Env>(e));
+        }};
+
+        using new_sender_type =
+            ::std::remove_cvref_t<decltype(new_sender(::std::forward<Sender>(sender), ::std::forward<Env>(env)))>;
+        using decayed_env = ::std::remove_cvref_t<Env>;
+
+        if constexpr (requires { typename new_sender_type::completion_behaviour; }) {
+            return typename new_sender_type::completion_behaviour{};
+        } else if constexpr (requires { ::std::move(new_sender).get_completion_behaviour(std::forward<Env>(env)); }) {
+            return std::move(new_sender).get_completion_behaviour(std::forward<Env>(env));
+        } else if constexpr (::beman::execution26::detail::is_awaitable<
+                                 new_sender_type,
+                                 ::beman::execution26::detail::env_promise<decayed_env>>) {
+            if (new_sender(sender, env).await_ready()) {
+                return completion_behaviour::inline_completion;
+            } else {
+                return completion_behaviour::unknown;
+            }
+        } else {
+            return completion_behaviour::unknown;
+        }
+    }
+};
+
+inline constexpr get_completion_behaviour_t get_completion_behaviour{};
+
+} // namespace beman::execution26
+
+#endif
diff --git a/include/beman/execution26/detail/just.hpp b/include/beman/execution26/detail/just.hpp
index 8296e87d..dc3ef22c 100644
--- a/include/beman/execution26/detail/just.hpp
+++ b/include/beman/execution26/detail/just.hpp
@@ -22,8 +22,8 @@
 
 namespace beman::execution26::detail {
 template <typename Completion, typename... T>
-concept just_size = (not::std::same_as<Completion, ::beman::execution26::set_error_t> or 1u == sizeof...(T)) &&
-                    (not::std::same_as<Completion, ::beman::execution26::set_stopped_t> or 0u == sizeof...(T));
+concept just_size = (not ::std::same_as<Completion, ::beman::execution26::set_error_t> or 1u == sizeof...(T)) &&
+                    (not ::std::same_as<Completion, ::beman::execution26::set_stopped_t> or 0u == sizeof...(T));
 template <typename Completion>
 struct just_t {
     template <typename... T>
@@ -49,6 +49,10 @@ struct impls_for<just_t<Completion>> : ::beman::execution26::detail::default_imp
             Completion()(::std::move(receiver), ::std::move(state.template get<I>())...);
         }(::std::make_index_sequence<State::size()>{});
     };
+
+    static constexpr auto get_completion_behaviour = [](const auto&, const auto&, const auto&) {
+        return ::beman::execution26::completion_behaviour::inline_completion;
+    };
 };
 } // namespace beman::execution26::detail
 
diff --git a/src/beman/execution26/CMakeLists.txt b/src/beman/execution26/CMakeLists.txt
index 1c02b30a..343aed1f 100644
--- a/src/beman/execution26/CMakeLists.txt
+++ b/src/beman/execution26/CMakeLists.txt
@@ -53,6 +53,7 @@ target_sources(
          ${PROJECT_SOURCE_DIR}/include/beman/execution26/detail/child_type.hpp
          ${PROJECT_SOURCE_DIR}/include/beman/execution26/detail/class_type.hpp
          ${PROJECT_SOURCE_DIR}/include/beman/execution26/detail/common.hpp
+         ${PROJECT_SOURCE_DIR}/include/beman/execution26/detail/completion_behaviour.hpp
          ${PROJECT_SOURCE_DIR}/include/beman/execution26/detail/completion_domain.hpp
          ${PROJECT_SOURCE_DIR}/include/beman/execution26/detail/completion_signature.hpp
          ${PROJECT_SOURCE_DIR}/include/beman/execution26/detail/completion_signatures.hpp
@@ -84,6 +85,7 @@ target_sources(
          ${PROJECT_SOURCE_DIR}/include/beman/execution26/detail/gather_signatures.hpp
          ${PROJECT_SOURCE_DIR}/include/beman/execution26/detail/get_allocator.hpp
          ${PROJECT_SOURCE_DIR}/include/beman/execution26/detail/get_awaiter.hpp
+         ${PROJECT_SOURCE_DIR}/include/beman/execution26/detail/get_completion_behaviour.hpp
          ${PROJECT_SOURCE_DIR}/include/beman/execution26/detail/get_completion_scheduler.hpp
          ${PROJECT_SOURCE_DIR}/include/beman/execution26/detail/get_completion_signatures.hpp
          ${PROJECT_SOURCE_DIR}/include/beman/execution26/detail/get_delegation_scheduler.hpp
diff --git a/tests/beman/execution26/CMakeLists.txt b/tests/beman/execution26/CMakeLists.txt
index b9130f6e..4dee7c6b 100644
--- a/tests/beman/execution26/CMakeLists.txt
+++ b/tests/beman/execution26/CMakeLists.txt
@@ -23,6 +23,7 @@ list(
   exec-general.test
   exec-get-allocator.test
   exec-get-compl-sched.test
+  exec-get-completion-behaviour.test
   exec-get-delegation-scheduler.test
   exec-get-domain.test
   exec-get-env.test
diff --git a/tests/beman/execution26/exec-get-completion-behaviour.test.cpp b/tests/beman/execution26/exec-get-completion-behaviour.test.cpp
new file mode 100644
index 00000000..9a021729
--- /dev/null
+++ b/tests/beman/execution26/exec-get-completion-behaviour.test.cpp
@@ -0,0 +1,53 @@
+// src/beman/execution26/tests/exec-get-completion-behaviour.test.cpp -*-C++-*-
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+#include <beman/execution26/detail/get_completion_behaviour.hpp>
+
+#include <test/execution.hpp>
+
+#include <type_traits>
+
+namespace {
+
+template <auto Value>
+using value = std::integral_constant<decltype(Value), Value>;
+
+struct awaitable {
+    static constexpr auto await_ready() noexcept -> bool { return true; }
+    auto                  await_suspend(auto parent) noexcept { return parent; }
+    auto                  await_resume() noexcept -> void {}
+};
+
+void test_constexpr_awaitable() {
+    auto completion_behaviour = value<test_std::get_completion_behaviour(awaitable{})>{};
+    ASSERT(test_std::completion_behaviour::inline_completion == completion_behaviour);
+}
+struct sender {
+    using completion_behaviour = value<test_std::completion_behaviour::inline_completion>;
+};
+
+struct sender2 {
+    static constexpr auto get_completion_behaviour() noexcept -> test_std::completion_behaviour {
+        return test_std::completion_behaviour::inline_completion;
+    }
+};
+
+void test_typedef_sender() {
+    auto completion_behaviour =
+        std::integral_constant<test_std::completion_behaviour, test_std::get_completion_behaviour(sender{})>{};
+    ASSERT(test_std::completion_behaviour::inline_completion == completion_behaviour);
+}
+
+void test_constexpr_sender() {
+    auto completion_behaviour =
+        std::integral_constant<test_std::completion_behaviour, test_std::get_completion_behaviour(sender{})>{};
+    ASSERT(test_std::completion_behaviour::inline_completion == completion_behaviour);
+}
+
+} // namespace
+
+TEST(exec_get_completion_behaviour) {
+    test_constexpr_awaitable();
+    test_typedef_sender();
+    test_constexpr_sender();
+}

From 068398039fb8a0de870bb1a345f6b0c8ea122609 Mon Sep 17 00:00:00 2001
From: Maikel Nadolski <maikel.nadolski@gmail.com>
Date: Wed, 8 Jan 2025 15:01:02 +0100
Subject: [PATCH 2/5] Fix test for just sender

---
 .../execution26/detail/get_completion_behaviour.hpp    | 10 +++++++---
 include/beman/execution26/detail/just.hpp              |  2 +-
 .../execution26/exec-get-completion-behaviour.test.cpp |  8 ++++++++
 3 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/include/beman/execution26/detail/get_completion_behaviour.hpp b/include/beman/execution26/detail/get_completion_behaviour.hpp
index bd2e4b53..3ed2b5ff 100644
--- a/include/beman/execution26/detail/get_completion_behaviour.hpp
+++ b/include/beman/execution26/detail/get_completion_behaviour.hpp
@@ -45,12 +45,16 @@ struct get_completion_behaviour_t {
 
         if constexpr (requires { typename new_sender_type::completion_behaviour; }) {
             return typename new_sender_type::completion_behaviour{};
-        } else if constexpr (requires { ::std::move(new_sender).get_completion_behaviour(std::forward<Env>(env)); }) {
-            return std::move(new_sender).get_completion_behaviour(std::forward<Env>(env));
+        } else if constexpr (requires {
+                                 new_sender(::std::forward<Sender>(sender), ::std::forward<Env>(env))
+                                     .get_completion_behaviour(std::forward<Env>(env));
+                             }) {
+            return new_sender(::std::forward<Sender>(sender), ::std::forward<Env>(env))
+                .get_completion_behaviour(std::forward<Env>(env));
         } else if constexpr (::beman::execution26::detail::is_awaitable<
                                  new_sender_type,
                                  ::beman::execution26::detail::env_promise<decayed_env>>) {
-            if (new_sender(sender, env).await_ready()) {
+            if (new_sender(::std::forward<Sender>(sender), ::std::forward<Env>(env)).await_ready()) {
                 return completion_behaviour::inline_completion;
             } else {
                 return completion_behaviour::unknown;
diff --git a/include/beman/execution26/detail/just.hpp b/include/beman/execution26/detail/just.hpp
index dc3ef22c..c7dfb601 100644
--- a/include/beman/execution26/detail/just.hpp
+++ b/include/beman/execution26/detail/just.hpp
@@ -50,7 +50,7 @@ struct impls_for<just_t<Completion>> : ::beman::execution26::detail::default_imp
         }(::std::make_index_sequence<State::size()>{});
     };
 
-    static constexpr auto get_completion_behaviour = [](const auto&, const auto&, const auto&) {
+    static constexpr auto get_completion_behaviour = [](const auto&, const auto&, const auto&...) {
         return ::beman::execution26::completion_behaviour::inline_completion;
     };
 };
diff --git a/tests/beman/execution26/exec-get-completion-behaviour.test.cpp b/tests/beman/execution26/exec-get-completion-behaviour.test.cpp
index 9a021729..79219851 100644
--- a/tests/beman/execution26/exec-get-completion-behaviour.test.cpp
+++ b/tests/beman/execution26/exec-get-completion-behaviour.test.cpp
@@ -2,6 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <beman/execution26/detail/get_completion_behaviour.hpp>
+#include <beman/execution26/detail/just.hpp>
 
 #include <test/execution.hpp>
 
@@ -44,10 +45,17 @@ void test_constexpr_sender() {
     ASSERT(test_std::completion_behaviour::inline_completion == completion_behaviour);
 }
 
+void test_just() {
+    auto just                 = test_std::just();
+    auto completion_behaviour = test_std::get_completion_behaviour(just, test_std::empty_env{});
+    ASSERT(test_std::completion_behaviour::inline_completion == completion_behaviour);
+}
+
 } // namespace
 
 TEST(exec_get_completion_behaviour) {
     test_constexpr_awaitable();
     test_typedef_sender();
     test_constexpr_sender();
+    test_just();
 }

From 37cb03855885e79a21217638c5edb87739a55310 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Dietmar=20K=C3=BChl?= <dietmar.kuehl@me.com>
Date: Sun, 12 Jan 2025 19:59:40 +0000
Subject: [PATCH 3/5] applied some fixes

---
 .../beman/execution26/detail/basic_sender.hpp | 21 +++++++++++++++++--
 .../execution26/detail/default_impls.hpp      |  1 +
 2 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/include/beman/execution26/detail/basic_sender.hpp b/include/beman/execution26/detail/basic_sender.hpp
index ae7a2e65..34853688 100644
--- a/include/beman/execution26/detail/basic_sender.hpp
+++ b/include/beman/execution26/detail/basic_sender.hpp
@@ -12,7 +12,7 @@
 #include <beman/execution26/detail/sender.hpp>
 #include <beman/execution26/detail/sender_decompose.hpp>
 #include <beman/execution26/detail/connect.hpp>
-#include <beman/execution26/detail/get_completion_signatures.hpp>
+#include <beman/execution26/detail/get_completion_behaviour.hpp>
 #include <utility>
 
 #include <beman/execution26/detail/suppress_push.hpp>
@@ -39,7 +39,23 @@ struct basic_sender : ::beman::execution26::detail::product_type<Tag, Data, Chil
             data.children);
     }
 
-    template <class Self, class Env>
+#if __cpp_explicit_this_parameter < 302110L //-dk:TODO need to figure out how to use explicit this with forwarding
+    template <class Env>
+    constexpr auto get_completion_behaviour(Env&& env) noexcept -> decltype(auto) {
+        return []<typename Self>(Self&& self, Env&& env) ->decltype(auto) {
+            auto data{::beman::execution26::detail::get_sender_data(self)};
+            return ::std::apply(
+                [&data, &env](auto&&... cs) {
+                    return ::beman::execution26::detail::impls_for<Tag>::get_completion_behaviour(
+                        ::std::forward<Env>(env),
+                        ::beman::execution26::detail::forward_like<Self>(data.data),
+                        ::beman::execution26::detail::forward_like<Self>(cs)...);
+                },
+                ::beman::execution26::detail::forward_like<Self>(data.children));
+            }(*this, ::std::forward<Env>(env));
+    }
+#else
+    template <class Env>
     constexpr auto get_completion_behaviour(this Self&& self, Env&& env) noexcept -> decltype(auto) {
         auto data{::beman::execution26::detail::get_sender_data(self)};
         return ::std::apply(
@@ -51,6 +67,7 @@ struct basic_sender : ::beman::execution26::detail::product_type<Tag, Data, Chil
             },
             ::beman::execution26::detail::forward_like<Self>(data.children));
     }
+#endif
 
     template <typename Receiver>
         requires(not ::beman::execution26::receiver<Receiver>)
diff --git a/include/beman/execution26/detail/default_impls.hpp b/include/beman/execution26/detail/default_impls.hpp
index f521d03d..e7471100 100644
--- a/include/beman/execution26/detail/default_impls.hpp
+++ b/include/beman/execution26/detail/default_impls.hpp
@@ -14,6 +14,7 @@
 #include <beman/execution26/detail/product_type.hpp>
 #include <beman/execution26/detail/sender_decompose.hpp>
 #include <beman/execution26/detail/start.hpp>
+#include <beman/execution26/detail/get_completion_behaviour.hpp>
 
 #include <utility>
 

From 0a41d6f976c7baffed1c9dd4f626f6ab73f067d3 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Dietmar=20K=C3=BChl?= <dietmar.kuehl@me.com>
Date: Sun, 12 Jan 2025 20:16:53 +0000
Subject: [PATCH 4/5] clang-format

---
 .../beman/execution26/detail/basic_sender.hpp | 20 +++++++++----------
 include/beman/execution26/detail/just.hpp     |  4 ++--
 2 files changed, 12 insertions(+), 12 deletions(-)

diff --git a/include/beman/execution26/detail/basic_sender.hpp b/include/beman/execution26/detail/basic_sender.hpp
index 34853688..04854fef 100644
--- a/include/beman/execution26/detail/basic_sender.hpp
+++ b/include/beman/execution26/detail/basic_sender.hpp
@@ -42,7 +42,7 @@ struct basic_sender : ::beman::execution26::detail::product_type<Tag, Data, Chil
 #if __cpp_explicit_this_parameter < 302110L //-dk:TODO need to figure out how to use explicit this with forwarding
     template <class Env>
     constexpr auto get_completion_behaviour(Env&& env) noexcept -> decltype(auto) {
-        return []<typename Self>(Self&& self, Env&& env) ->decltype(auto) {
+        return []<typename Self>(Self&& self, Env&& env) -> decltype(auto) {
             auto data{::beman::execution26::detail::get_sender_data(self)};
             return ::std::apply(
                 [&data, &env](auto&&... cs) {
@@ -52,7 +52,7 @@ struct basic_sender : ::beman::execution26::detail::product_type<Tag, Data, Chil
                         ::beman::execution26::detail::forward_like<Self>(cs)...);
                 },
                 ::beman::execution26::detail::forward_like<Self>(data.children));
-            }(*this, ::std::forward<Env>(env));
+        }(*this, ::std::forward<Env>(env));
     }
 #else
     template <class Env>
@@ -70,15 +70,15 @@ struct basic_sender : ::beman::execution26::detail::product_type<Tag, Data, Chil
 #endif
 
     template <typename Receiver>
-        requires(not ::beman::execution26::receiver<Receiver>)
+        requires(not::beman::execution26::receiver<Receiver>)
     auto connect(Receiver receiver) = BEMAN_EXECUTION26_DELETE("the passed receiver doesn't model receiver");
 
   private:
 #if __cpp_explicit_this_parameter < 302110L //-dk:TODO need to figure out how to use explicit this with forwarding
     template <::beman::execution26::receiver Receiver>
     auto connect(Receiver receiver) & noexcept(
-        noexcept(::beman::execution26::detail::basic_operation<basic_sender&, Receiver>{
-            *this, ::std::move(receiver)})) -> ::beman::execution26::detail::basic_operation<basic_sender&, Receiver> {
+        noexcept(::beman::execution26::detail::basic_operation<basic_sender&, Receiver>{*this, ::std::move(receiver)}))
+        -> ::beman::execution26::detail::basic_operation<basic_sender&, Receiver> {
         return {*this, ::std::move(receiver)};
     }
     template <::beman::execution26::receiver Receiver>
@@ -89,9 +89,9 @@ struct basic_sender : ::beman::execution26::detail::product_type<Tag, Data, Chil
     }
     template <::beman::execution26::receiver Receiver>
     auto connect(Receiver receiver) && noexcept(
-        noexcept(::beman::execution26::detail::basic_operation<basic_sender, Receiver>{
-            ::std::move(*this),
-            ::std::move(receiver)})) -> ::beman::execution26::detail::basic_operation<basic_sender, Receiver> {
+        noexcept(::beman::execution26::detail::basic_operation<basic_sender, Receiver>{::std::move(*this),
+                                                                                       ::std::move(receiver)}))
+        -> ::beman::execution26::detail::basic_operation<basic_sender, Receiver> {
         return {::std::move(*this), ::std::move(receiver)};
     }
 #else
@@ -99,8 +99,8 @@ struct basic_sender : ::beman::execution26::detail::product_type<Tag, Data, Chil
     auto
     connect(this Self&& self,
             Receiver receiver) noexcept(noexcept(::beman::execution26::detail::basic_operation<basic_sender, Receiver>{
-        ::std::forward<Self>(self),
-        ::std::move(receiver)})) -> ::beman::execution26::detail::basic_operation<Self, Receiver> {
+        ::std::forward<Self>(self), ::std::move(receiver)}))
+        -> ::beman::execution26::detail::basic_operation<Self, Receiver> {
         return {::std::forward<Self>(self), ::std::move(receiver)};
     }
 #endif
diff --git a/include/beman/execution26/detail/just.hpp b/include/beman/execution26/detail/just.hpp
index c7dfb601..7a837a9a 100644
--- a/include/beman/execution26/detail/just.hpp
+++ b/include/beman/execution26/detail/just.hpp
@@ -22,8 +22,8 @@
 
 namespace beman::execution26::detail {
 template <typename Completion, typename... T>
-concept just_size = (not ::std::same_as<Completion, ::beman::execution26::set_error_t> or 1u == sizeof...(T)) &&
-                    (not ::std::same_as<Completion, ::beman::execution26::set_stopped_t> or 0u == sizeof...(T));
+concept just_size = (not::std::same_as<Completion, ::beman::execution26::set_error_t> or 1u == sizeof...(T)) &&
+                    (not::std::same_as<Completion, ::beman::execution26::set_stopped_t> or 0u == sizeof...(T));
 template <typename Completion>
 struct just_t {
     template <typename... T>

From 0827385b5ed3e651aa0fa4da4def449fc61685c8 Mon Sep 17 00:00:00 2001
From: Maikel Nadolski <maikel.nadolski@gmail.com>
Date: Mon, 13 Jan 2025 09:55:58 +0100
Subject: [PATCH 5/5] More constexpr

---
 .../beman/execution26/detail/forward_like.hpp | 14 +++++------
 .../detail/get_completion_behaviour.hpp       |  3 ++-
 include/beman/execution26/detail/just.hpp     |  6 ++---
 .../beman/execution26/detail/product_type.hpp | 24 ++++++++++---------
 .../execution26/detail/sender_decompose.hpp   |  4 ++--
 .../exec-get-completion-behaviour.test.cpp    |  6 +++++
 6 files changed, 33 insertions(+), 24 deletions(-)

diff --git a/include/beman/execution26/detail/forward_like.hpp b/include/beman/execution26/detail/forward_like.hpp
index 4b958901..5192cb36 100644
--- a/include/beman/execution26/detail/forward_like.hpp
+++ b/include/beman/execution26/detail/forward_like.hpp
@@ -18,35 +18,35 @@ struct forward_like_helper;
 template <typename T>
 struct forward_like_helper {
     template <typename U>
-    static auto forward(U&& u) -> ::std::remove_reference_t<U>&& {
+    static constexpr auto forward(U&& u) -> ::std::remove_reference_t<U>&& {
         return ::std::move(u); // NOLINT(bugprone-move-forwarding-reference)
     }
 };
 template <typename T>
 struct forward_like_helper<T&&> {
     template <typename U>
-    static auto forward(U&& u) -> ::std::remove_cvref_t<U>&& {
+    static constexpr auto forward(U&& u) -> ::std::remove_cvref_t<U>&& {
         return ::std::move(u); // NOLINT(bugprone-move-forwarding-reference)
     }
 };
 template <typename T>
 struct forward_like_helper<T&> {
     template <typename U>
-    static auto forward(U&& u) -> ::std::remove_cvref_t<U>& {
+    static constexpr auto forward(U&& u) -> ::std::remove_cvref_t<U>& {
         return ::std::forward<U&&>(u);
     }
 };
 template <typename T>
 struct forward_like_helper<const T&&> {
     template <typename U>
-    static auto forward(U&& u) -> const ::std::remove_cvref_t<U>&& {
+    static constexpr auto forward(U&& u) -> const ::std::remove_cvref_t<U>&& {
         return ::std::move(u); // NOLINT(bugprone-move-forwarding-reference)
     }
 };
 template <typename T>
 struct forward_like_helper<const T&> {
     template <typename U>
-    static auto forward(U&& u) -> const ::std::remove_cvref_t<U>& {
+    static constexpr auto forward(U&& u) -> const ::std::remove_cvref_t<U>& {
         return ::std::forward<U&&>(u);
     }
 };
@@ -54,7 +54,7 @@ struct forward_like_helper<const T&> {
 // The overload own_forward_like is used for testing on systems
 // which actually do provide an implementation.
 template <typename T, typename U>
-auto own_forward_like(U&& u) noexcept -> decltype(auto) {
+constexpr auto own_forward_like(U&& u) noexcept -> decltype(auto) {
     return ::beman::execution26::detail::forward_like_helper<T>::forward(::std::forward<U>(u));
 }
 
@@ -64,7 +64,7 @@ auto own_forward_like(U&& u) noexcept -> decltype(auto) {
  * \internal
  */
 template <typename T, typename U>
-auto forward_like(U&& u) noexcept -> decltype(auto) {
+constexpr auto forward_like(U&& u) noexcept -> decltype(auto) {
 #if 202207 <= disabled__cpp_lib_forward_like
     return ::std::forward_like<T>(::std::forward<U>(u));
 #else
diff --git a/include/beman/execution26/detail/get_completion_behaviour.hpp b/include/beman/execution26/detail/get_completion_behaviour.hpp
index 3ed2b5ff..0b002790 100644
--- a/include/beman/execution26/detail/get_completion_behaviour.hpp
+++ b/include/beman/execution26/detail/get_completion_behaviour.hpp
@@ -49,7 +49,8 @@ struct get_completion_behaviour_t {
                                  new_sender(::std::forward<Sender>(sender), ::std::forward<Env>(env))
                                      .get_completion_behaviour(std::forward<Env>(env));
                              }) {
-            return new_sender(::std::forward<Sender>(sender), ::std::forward<Env>(env))
+            std::remove_cvref_t<Env> copiedEnv(env);
+            return new_sender(::std::forward<Sender>(sender), ::std::forward<Env>(copiedEnv))
                 .get_completion_behaviour(std::forward<Env>(env));
         } else if constexpr (::beman::execution26::detail::is_awaitable<
                                  new_sender_type,
diff --git a/include/beman/execution26/detail/just.hpp b/include/beman/execution26/detail/just.hpp
index 7a837a9a..6b93d57d 100644
--- a/include/beman/execution26/detail/just.hpp
+++ b/include/beman/execution26/detail/just.hpp
@@ -22,14 +22,14 @@
 
 namespace beman::execution26::detail {
 template <typename Completion, typename... T>
-concept just_size = (not::std::same_as<Completion, ::beman::execution26::set_error_t> or 1u == sizeof...(T)) &&
-                    (not::std::same_as<Completion, ::beman::execution26::set_stopped_t> or 0u == sizeof...(T));
+concept just_size = (not ::std::same_as<Completion, ::beman::execution26::set_error_t> or 1u == sizeof...(T)) &&
+                    (not ::std::same_as<Completion, ::beman::execution26::set_stopped_t> or 0u == sizeof...(T));
 template <typename Completion>
 struct just_t {
     template <typename... T>
         requires ::beman::execution26::detail::just_size<Completion, T...> &&
                  (::std::movable<::std::decay_t<T>> && ...)
-    auto operator()(T&&... arg) const {
+    constexpr auto operator()(T&&... arg) const {
         return ::beman::execution26::detail::make_sender(
             *this, ::beman::execution26::detail::product_type{::std::forward<T>(arg)...});
     }
diff --git a/include/beman/execution26/detail/product_type.hpp b/include/beman/execution26/detail/product_type.hpp
index b309f95c..ee520a51 100644
--- a/include/beman/execution26/detail/product_type.hpp
+++ b/include/beman/execution26/detail/product_type.hpp
@@ -29,34 +29,35 @@ struct product_type_base<::std::index_sequence<I...>, T...>
     static constexpr bool          is_product_type{true};
 
     template <::std::size_t J, typename S>
-    static auto element_get(::beman::execution26::detail::product_type_element<J, S>& self) noexcept -> S& {
+    static constexpr auto element_get(::beman::execution26::detail::product_type_element<J, S>& self) noexcept -> S& {
         return self.value;
     }
     template <::std::size_t J, typename S>
-    static auto element_get(::beman::execution26::detail::product_type_element<J, S>&& self) noexcept -> S&& {
+    static constexpr auto
+    element_get(::beman::execution26::detail::product_type_element<J, S>&& self) noexcept -> S&& {
         return ::std::move(self.value);
     }
     template <::std::size_t J, typename S>
-    static auto element_get(const ::beman::execution26::detail::product_type_element<J, S>& self) noexcept
-        -> const S& {
+    static constexpr auto
+    element_get(const ::beman::execution26::detail::product_type_element<J, S>& self) noexcept -> const S& {
         return self.value;
     }
 
     template <::std::size_t J>
-    auto get() & -> decltype(auto) {
+    constexpr auto get() & -> decltype(auto) {
         return this->element_get<J>(*this);
     }
     template <::std::size_t J>
-    auto get() && -> decltype(auto) {
+    constexpr auto get() && -> decltype(auto) {
         return this->element_get<J>(::std::move(*this));
     }
     template <::std::size_t J>
-    auto get() const& -> decltype(auto) {
+    constexpr auto get() const& -> decltype(auto) {
         return this->element_get<J>(*this);
     }
 
     template <::std::size_t J, typename Allocator, typename Self>
-    static auto make_element(Allocator&& alloc, Self&& self) -> decltype(auto) {
+    static constexpr auto make_element(Allocator&& alloc, Self&& self) -> decltype(auto) {
         using type = ::std::remove_cvref_t<decltype(product_type_base::element_get<J>(std::forward<Self>(self)))>;
         if constexpr (::std::uses_allocator_v<type, Allocator>)
             return ::std::make_obj_using_allocator<type>(alloc,
@@ -65,7 +66,7 @@ struct product_type_base<::std::index_sequence<I...>, T...>
             return product_type_base::element_get<J>(std::forward<Self>(self));
     }
 
-    auto operator==(const product_type_base&) const -> bool = default;
+    constexpr auto operator==(const product_type_base&) const -> bool = default;
 };
 
 template <typename T>
@@ -74,12 +75,13 @@ concept is_product_type_c = requires(const T& t) { T::is_product_type; };
 template <typename... T>
 struct product_type : ::beman::execution26::detail::product_type_base<::std::index_sequence_for<T...>, T...> {
     template <typename Allocator, typename Product, std::size_t... I>
-    static auto make_from(Allocator&& allocator, Product&& product, std::index_sequence<I...>) -> product_type {
+    static constexpr auto
+    make_from(Allocator&& allocator, Product&& product, std::index_sequence<I...>) -> product_type {
         return {product_type::template make_element<I>(allocator, ::std::forward<Product>(product))...};
     }
 
     template <typename Allocator, typename Product>
-    static auto make_from(Allocator&& allocator, Product&& product) -> product_type {
+    static constexpr auto make_from(Allocator&& allocator, Product&& product) -> product_type {
         return product_type::make_from(
             ::std::forward<Allocator>(allocator), ::std::forward<Product>(product), ::std::index_sequence_for<T...>{});
     }
diff --git a/include/beman/execution26/detail/sender_decompose.hpp b/include/beman/execution26/detail/sender_decompose.hpp
index d8915f54..0c801aa5 100644
--- a/include/beman/execution26/detail/sender_decompose.hpp
+++ b/include/beman/execution26/detail/sender_decompose.hpp
@@ -35,7 +35,7 @@ struct sender_data {
 };
 
 template <typename Sender>
-auto get_sender_data(Sender&& sender) {
+constexpr auto get_sender_data(Sender&& sender) {
 #if 0
         //-dk:TODO should use a dynamic/language approach:
         auto&& [tag, data, ... children] = sender;
@@ -82,7 +82,7 @@ auto get_sender_data(Sender&& sender) {
 }
 
 template <typename Sender>
-auto get_sender_meta(Sender&& sender) {
+constexpr auto get_sender_meta(Sender&& sender) {
     using type = decltype(get_sender_data(sender));
     return sender_meta<typename type::tag_type, typename type::data_type, typename type::children_type>{};
 }
diff --git a/tests/beman/execution26/exec-get-completion-behaviour.test.cpp b/tests/beman/execution26/exec-get-completion-behaviour.test.cpp
index 79219851..44eff6fe 100644
--- a/tests/beman/execution26/exec-get-completion-behaviour.test.cpp
+++ b/tests/beman/execution26/exec-get-completion-behaviour.test.cpp
@@ -51,6 +51,11 @@ void test_just() {
     ASSERT(test_std::completion_behaviour::inline_completion == completion_behaviour);
 }
 
+void test_constexpr_just() {
+    constexpr auto completion_behaviour = test_std::get_completion_behaviour(test_std::just(), test_std::empty_env{});
+    ASSERT(test_std::completion_behaviour::inline_completion == completion_behaviour);
+}
+
 } // namespace
 
 TEST(exec_get_completion_behaviour) {
@@ -58,4 +63,5 @@ TEST(exec_get_completion_behaviour) {
     test_typedef_sender();
     test_constexpr_sender();
     test_just();
+    test_constexpr_just();
 }