From b828823fc0dbe6ebee517a9ea26a067e2fea67c0 Mon Sep 17 00:00:00 2001
From: Cra3z <CrazyCra3z@outlook.com>
Date: Mon, 21 Sep 2026 13:27:45 +0800
Subject: [PATCH 1/5] Fix `on` and `continues_on`

---
 .../beman/execution/detail/continues_on.hpp   |  17 ++-
 include/beman/execution/detail/on.hpp         | 100 ++++++++++--------
 2 files changed, 69 insertions(+), 48 deletions(-)

diff --git a/include/beman/execution/detail/continues_on.hpp b/include/beman/execution/detail/continues_on.hpp
index 30242eb4..39477c2a 100644
--- a/include/beman/execution/detail/continues_on.hpp
+++ b/include/beman/execution/detail/continues_on.hpp
@@ -50,6 +50,7 @@ import beman.execution.detail.sender;
 import beman.execution.detail.sender_adaptor_closure;
 import beman.execution.detail.sender_for;
 import beman.execution.detail.sender_in;
+import beman.execution.detail.sends_stopped;
 import beman.execution.detail.set_error;
 import beman.execution.detail.set_stopped;
 import beman.execution.detail.set_value;
@@ -84,6 +85,7 @@ import beman.execution.detail.start;
 #include <beman/execution/detail/sender_adaptor.hpp>
 #include <beman/execution/detail/sender_for.hpp>
 #include <beman/execution/detail/sender_in.hpp>
+#include <beman/execution/detail/sends_stopped.hpp>
 #include <beman/execution/detail/set_error.hpp>
 #include <beman/execution/detail/set_stopped.hpp>
 #include <beman/execution/detail/set_value.hpp>
@@ -119,13 +121,18 @@ struct continues_on_t {
     struct get_signatures<
         ::beman::execution::detail::basic_sender<::beman::execution::detail::continues_on_t, Scheduler, Sender>,
         Env> {
-        using scheduler_sender = ::beman::execution::schedule_result_t<Scheduler>;
+        using scheduler_sender      = ::beman::execution::schedule_result_t<Scheduler>;
+        using additional_signatures = ::std::conditional_t<
+            ::beman::execution::sends_stopped<scheduler_sender>,
+            ::beman::execution::completion_signatures<::beman::execution::set_error_t(::std::exception_ptr),
+                                                      ::beman::execution::set_stopped_t()>,
+            ::beman::execution::completion_signatures<::beman::execution::set_error_t(::std::exception_ptr)>>;
         template <typename... E>
         using as_set_error = ::beman::execution::completion_signatures<::beman::execution::set_error_t(E)...>;
-        using type         = ::beman::execution::detail::meta::combine<
-            decltype(::beman::execution::get_completion_signatures<Sender, Env>()),
-            ::beman::execution::error_types_of_t<scheduler_sender, Env, as_set_error>,
-            ::beman::execution::completion_signatures<::beman::execution::set_error_t(::std::exception_ptr)>>;
+        using type         = ::beman::execution::detail::meta::unique<::beman::execution::detail::meta::combine<
+                    decltype(::beman::execution::get_completion_signatures<Sender, Env>()),
+                    ::beman::execution::error_types_of_t<scheduler_sender, Env, as_set_error>,
+                    additional_signatures>>;
     };
 
     template <typename Scheduler, typename ChildAttrs>
diff --git a/include/beman/execution/detail/on.hpp b/include/beman/execution/detail/on.hpp
index fec57ba4..2724da98 100644
--- a/include/beman/execution/detail/on.hpp
+++ b/include/beman/execution/detail/on.hpp
@@ -60,49 +60,27 @@ import beman.execution.detail.transform_sender;
 
 namespace beman::execution::detail {
 struct on_t : ::beman::execution::sender_adaptor_closure<on_t> {
-    template <typename>
-    struct env_needs_get_start_scheduler {
-        using sender_concept = ::beman::execution::sender_tag;
-        template <typename, typename Env>
-        static constexpr auto get_completion_signatures() {
-            return env_needs_get_start_scheduler<Env>{};
-        }
-    };
-
     template <::beman::execution::detail::sender_for<on_t> OutSndr, typename Env>
-    auto transform_sender(::beman::execution::set_value_t, OutSndr&& out_sndr, const Env& env) const
+    static auto transform_sender(::beman::execution::set_value_t, OutSndr&& out_sndr, const Env& env)
         -> decltype(auto) {
-        struct not_a_scheduler_t {};
         auto&& data  = out_sndr.template get<1>();
         auto&& child = out_sndr.template get<2>();
 
         if constexpr (::beman::execution::scheduler<decltype(data)>) {
-            auto sch{::beman::execution::detail::query_with_default(
-                ::beman::execution::get_start_scheduler, env, not_a_scheduler_t{})};
-            if constexpr (::std::same_as<not_a_scheduler_t, decltype(sch)>) {
-                return env_needs_get_start_scheduler<Env>{};
-            } else {
-                return ::beman::execution::continues_on(
-                    ::beman::execution::starts_on(::beman::execution::detail::forward_like<OutSndr>(data),
-                                                  ::beman::execution::detail::forward_like<OutSndr>(child)),
-                    ::std::move(sch));
-            }
+            auto start_sch = ::beman::execution::get_start_scheduler(env);
+            return ::beman::execution::continues_on(
+                ::beman::execution::starts_on(::beman::execution::detail::forward_like<OutSndr>(data),
+                                              ::beman::execution::detail::forward_like<OutSndr>(child)),
+                ::std::move(start_sch));
         } else {
             auto& [sch, closure] = data;
-            auto orig_sch{::beman::execution::detail::call_with_default(
-                ::beman::execution::get_completion_scheduler<::beman::execution::set_value_t>,
-                not_a_scheduler_t{},
-                ::beman::execution::get_env(child),
-                env)};
-
-            if constexpr (::std::same_as<not_a_scheduler_t, decltype(orig_sch)>) {
-                return env_needs_get_start_scheduler<Env>{};
-            } else {
-                return ::beman::execution::continues_on(
-                    ::beman::execution::detail::forward_like<OutSndr>(closure)(::beman::execution::continues_on(
-                        ::beman::execution::detail::forward_like<OutSndr>(child), sch)),
-                    orig_sch);
-            }
+            auto orig_sch        = ::beman::execution::get_completion_scheduler<::beman::execution::set_value_t>(
+                ::beman::execution::get_env(child), env);
+
+            return ::beman::execution::continues_on(
+                ::beman::execution::detail::forward_like<OutSndr>(closure)(
+                    ::beman::execution::continues_on(::beman::execution::detail::forward_like<OutSndr>(child), sch)),
+                orig_sch);
         }
     }
 
@@ -116,7 +94,7 @@ struct on_t : ::beman::execution::sender_adaptor_closure<on_t> {
               ::beman::execution::detail::is_sender_adaptor_closure Closure>
         requires ::beman::execution::detail::is_sender_adaptor_closure<Sndr>
     auto operator()(Sndr&&, Sch&&, Closure&&) const -> void =
-        BEMAN_EXECUTION_DELETE("on(sch, sndr) requires that sndr isn't both a sender and sender adaptor closure");
+        BEMAN_EXECUTION_DELETE("on(sndr, sch, closure) requires that sndr isn't both a sender and sender adaptor closure");
 
     template <::beman::execution::scheduler Sch, ::beman::execution::sender Sndr>
     auto operator()(Sch&& sch, Sndr&& sndr) const {
@@ -138,15 +116,51 @@ struct on_t : ::beman::execution::sender_adaptor_closure<on_t> {
     }
     template <typename, typename...>
     struct get_signatures;
-    template <typename Data, ::beman::execution::sender Sndr, typename... Env>
-    struct get_signatures<::beman::execution::detail::basic_sender<::beman::execution::detail::on_t, Data, Sndr>,
-                          Env...> {
-        using type = ::beman::execution::completion_signatures_of_t<Sndr, Env...>;
+
+    /// for `on(scheduler, sender)`
+    template <typename Sched, typename Child, typename Env>
+    struct get_signatures<::beman::execution::detail::basic_sender<::beman::execution::detail::on_t, Sched, Child>,
+                          Env> {
+
+        static consteval auto get() noexcept
+            requires ::std::invocable<::beman::execution::get_start_scheduler_t, Env>
+        {
+            using transformed_sndr = decltype(on_t::transform_sender(
+                ::beman::execution::set_value,
+                ::std::declval<
+                    ::beman::execution::detail::basic_sender<::beman::execution::detail::on_t, Sched, Child>>(),
+                ::std::declval<Env>()));
+            return ::beman::execution::get_completion_signatures<transformed_sndr, Env>();
+        }
+    };
+
+    /// for `on(sender, scheduler, closure)`
+    template <typename Sched, typename Closure, typename Child, typename Env>
+    struct get_signatures<
+        ::beman::execution::detail::basic_sender<::beman::execution::detail::on_t,
+                                                 ::beman::execution::detail::product_type<Sched, Closure>,
+                                                 Child>,
+        Env> {
+        static constexpr auto get() noexcept
+            requires ::std::invocable<::beman::execution::get_completion_scheduler_t<::beman::execution::set_value_t>,
+                                      ::beman::execution::env_of_t<Child>,
+                                      Env>
+        {
+            using transformed_sndr = decltype(on_t::transform_sender(
+                ::beman::execution::set_value,
+                ::std::declval<
+                    ::beman::execution::detail::basic_sender<::beman::execution::detail::on_t,
+                                                             ::beman::execution::detail::product_type<Sched, Closure>,
+                                                             Child>>(),
+                ::std::declval<Env>()));
+            return ::beman::execution::get_completion_signatures<transformed_sndr, Env>();
+        }
     };
 
-    template <typename Sender, typename... Env>
-    static consteval auto get_completion_signatures() {
-        return typename get_signatures<std::remove_cvref_t<Sender>, Env...>::type{};
+    template <typename Sender, typename Env>
+        requires requires { get_signatures<std::remove_cvref_t<Sender>, Env>::get(); }
+    static consteval auto get_completion_signatures() noexcept {
+        return get_signatures<std::remove_cvref_t<Sender>, Env>::get();
     }
 };
 

From 802c9ccdf6f6a8711ab490138e1a262cae0dc659 Mon Sep 17 00:00:00 2001
From: Cra3z <CrazyCra3z@outlook.com>
Date: Mon, 21 Sep 2026 18:13:28 +0800
Subject: [PATCH 2/5] Fix some errors

---
 include/beman/execution/detail/on.hpp         | 135 +++++++++++++++++-
 include/beman/execution/detail/starts_on.hpp  |  34 ++---
 .../execution/exec-inline-scheduler.test.cpp  |   3 +-
 tests/beman/execution/exec-on.test.cpp        |  77 ++++++++--
 .../exec-parallel-scheduler.test.cpp          |  11 ++
 5 files changed, 220 insertions(+), 40 deletions(-)

diff --git a/include/beman/execution/detail/on.hpp b/include/beman/execution/detail/on.hpp
index 2724da98..17cfef6f 100644
--- a/include/beman/execution/detail/on.hpp
+++ b/include/beman/execution/detail/on.hpp
@@ -8,6 +8,7 @@
 #ifdef BEMAN_HAS_IMPORT_STD
 import std;
 #else
+#include <type_traits>
 #include <utility>
 #endif
 #ifdef BEMAN_HAS_MODULES
@@ -15,9 +16,13 @@ import beman.execution.detail.basic_sender;
 import beman.execution.detail.call_with_default;
 import beman.execution.detail.completion_signatures_of_t;
 import beman.execution.detail.continues_on;
+import beman.execution.detail.default_impls;
 import beman.execution.detail.default_domain;
+import beman.execution.detail.env_of_t;
 import beman.execution.detail.forward_like;
 import beman.execution.detail.fwd_env;
+import beman.execution.detail.get_completion_domain;
+import beman.execution.detail.get_completion_signatures;
 import beman.execution.detail.get_completion_scheduler;
 import beman.execution.detail.get_domain;
 import beman.execution.detail.get_env;
@@ -38,10 +43,16 @@ import beman.execution.detail.transform_sender;
 #include <beman/execution/detail/basic_sender.hpp>
 #include <beman/execution/detail/call_with_default.hpp>
 #include <beman/execution/detail/continues_on.hpp>
+#include <beman/execution/detail/default_impls.hpp>
 #include <beman/execution/detail/default_domain.hpp>
+#include <beman/execution/detail/env_of_t.hpp>
 #include <beman/execution/detail/forward_like.hpp>
 #include <beman/execution/detail/fwd_env.hpp>
+#include <beman/execution/detail/get_completion_domain.hpp>
+#include <beman/execution/detail/get_completion_signatures.hpp>
+#include <beman/execution/detail/get_completion_scheduler.hpp>
 #include <beman/execution/detail/get_domain.hpp>
+#include <beman/execution/detail/get_env.hpp>
 #include <beman/execution/detail/get_start_scheduler.hpp>
 #include <beman/execution/detail/join_env.hpp>
 #include <beman/execution/detail/make_sender.hpp>
@@ -60,7 +71,21 @@ import beman.execution.detail.transform_sender;
 
 namespace beman::execution::detail {
 struct on_t : ::beman::execution::sender_adaptor_closure<on_t> {
+    template <typename Env, typename OutSndr>
+    static auto dry_run(OutSndr&& out_sndr) noexcept {
+        auto& [_, data, child] = out_sndr;
+        if constexpr (::beman::execution::scheduler<decltype(data)>) {
+            return ::std::bool_constant<::std::invocable<::beman::execution::get_start_scheduler_t, Env>>{};
+        } else {
+            ::std::bool_constant<
+                ::std::invocable<::beman::execution::get_completion_scheduler_t<::beman::execution::set_value_t>,
+                                 ::beman::execution::env_of_t<decltype(child)>,
+                                 Env>>{};
+        }
+    }
+
     template <::beman::execution::detail::sender_for<on_t> OutSndr, typename Env>
+        requires(decltype(on_t::dry_run<Env>(::std::declval<OutSndr>()))::value)
     static auto transform_sender(::beman::execution::set_value_t, OutSndr&& out_sndr, const Env& env)
         -> decltype(auto) {
         auto&& data  = out_sndr.template get<1>();
@@ -84,6 +109,25 @@ struct on_t : ::beman::execution::sender_adaptor_closure<on_t> {
         }
     }
 
+    struct impls_for : ::beman::execution::detail::default_impls {
+        struct get_attrs_impl {
+            template <typename Sched, typename Child>
+            auto operator()(const Sched&, const Child& child) const noexcept {
+                using ChildAttrs = ::std::remove_cvref_t<::beman::execution::env_of_t<Child>>;
+                return attrs1<ChildAttrs>{::beman::execution::get_env(child)};
+            }
+
+            template <typename Sched, typename Closure, typename Child>
+            auto operator()(const ::beman::execution::detail::product_type<Sched, Closure>&,
+                            const Child& child) const noexcept {
+                using ChildAttrs = ::std::remove_cvref_t<::beman::execution::env_of_t<Child>>;
+                return attrs2<ChildAttrs>{::beman::execution::get_env(child)};
+            }
+        };
+
+        static constexpr auto get_attrs{get_attrs_impl{}};
+    };
+
     template <::beman::execution::scheduler Sch, ::beman::execution::sender Sndr>
         requires ::beman::execution::detail::is_sender_adaptor_closure<Sndr>
     auto operator()(Sch&&, Sndr&&) const -> void =
@@ -93,8 +137,8 @@ struct on_t : ::beman::execution::sender_adaptor_closure<on_t> {
               ::beman::execution::sender                            Sndr,
               ::beman::execution::detail::is_sender_adaptor_closure Closure>
         requires ::beman::execution::detail::is_sender_adaptor_closure<Sndr>
-    auto operator()(Sndr&&, Sch&&, Closure&&) const -> void =
-        BEMAN_EXECUTION_DELETE("on(sndr, sch, closure) requires that sndr isn't both a sender and sender adaptor closure");
+    auto operator()(Sndr&&, Sch&&, Closure&&) const -> void = BEMAN_EXECUTION_DELETE(
+        "on(sndr, sch, closure) requires that sndr isn't both a sender and sender adaptor closure");
 
     template <::beman::execution::scheduler Sch, ::beman::execution::sender Sndr>
     auto operator()(Sch&& sch, Sndr&& sndr) const {
@@ -114,6 +158,87 @@ struct on_t : ::beman::execution::sender_adaptor_closure<on_t> {
         return ::beman::execution::detail::make_sender_adaptor(
             *this, ::std::forward<Sch>(sch), ::std::forward<Closure>(closure));
     }
+
+  private:
+    template <typename>
+    struct is_completion_query : ::std::false_type {};
+
+    template <typename Tag>
+    struct is_completion_query<::beman::execution::get_completion_scheduler_t<Tag>> : ::std::true_type {};
+
+    template <typename Tag>
+    struct is_completion_query<::beman::execution::get_completion_domain_t<Tag>> : ::std::true_type {};
+
+    template <typename ChildAttrs>
+    struct attrs_base {
+        template <typename Query, typename... Args>
+            requires(!is_completion_query<::std::remove_cvref_t<Query>>::value) &&
+                    requires(const ChildAttrs& child_attrs, Query query, Args&&... args) {
+                        query(::beman::execution::detail::fwd_env(child_attrs), ::std::forward<Args>(args)...);
+                    }
+        auto query(Query query, Args&&... args) const noexcept {
+            return query(::beman::execution::detail::fwd_env(this->child_attrs), ::std::forward<Args>(args)...);
+        }
+
+        ChildAttrs child_attrs;
+    };
+
+    template <typename ChildAttrs>
+    struct attrs1 : attrs_base<ChildAttrs> {
+        using attrs_base<ChildAttrs>::query;
+
+        template <typename Tag, typename Env>
+            requires requires(const Env& env) {
+                ::beman::execution::get_completion_scheduler<Tag>(::beman::execution::get_start_scheduler(env),
+                                                                  ::beman::execution::detail::fwd_env(env));
+            }
+        auto query(::beman::execution::get_completion_scheduler_t<Tag>, const Env& env) const noexcept {
+            auto sched = ::beman::execution::get_start_scheduler(env);
+            return ::beman::execution::get_completion_scheduler<Tag>(sched, ::beman::execution::detail::fwd_env(env));
+        }
+
+        template <typename Tag, typename Env>
+            requires requires(const Env& env) {
+                ::beman::execution::get_completion_domain<Tag>(::beman::execution::get_start_scheduler(env),
+                                                               ::beman::execution::detail::fwd_env(env));
+            }
+        auto query(::beman::execution::get_completion_domain_t<Tag>, const Env& env) const noexcept {
+            auto sched = ::beman::execution::get_start_scheduler(env);
+            return ::beman::execution::get_completion_domain<Tag>(sched, ::beman::execution::detail::fwd_env(env));
+        }
+    };
+
+    template <typename ChildAttrs>
+    struct attrs2 : attrs_base<ChildAttrs> {
+        using attrs_base<ChildAttrs>::query;
+
+        template <typename Env>
+        auto original_sched(const Env& env) const noexcept {
+            return ::beman::execution::get_completion_scheduler<::beman::execution::set_value_t>(this->child_attrs,
+                                                                                                 env);
+        }
+
+        template <typename Tag, typename Env>
+            requires requires(const attrs2& self, const Env& env) {
+                ::beman::execution::get_completion_scheduler<Tag>(self.original_sched(env),
+                                                                  ::beman::execution::detail::fwd_env(env));
+            }
+        auto query(::beman::execution::get_completion_scheduler_t<Tag>, const Env& env) const noexcept {
+            return ::beman::execution::get_completion_scheduler<Tag>(this->original_sched(env),
+                                                                     ::beman::execution::detail::fwd_env(env));
+        }
+
+        template <typename Tag, typename Env>
+            requires requires(const attrs2& self, const Env& env) {
+                ::beman::execution::get_completion_domain<Tag>(self.original_sched(env),
+                                                               ::beman::execution::detail::fwd_env(env));
+            }
+        auto query(::beman::execution::get_completion_domain_t<Tag>, const Env& env) const noexcept {
+            return ::beman::execution::get_completion_domain<Tag>(this->original_sched(env),
+                                                                  ::beman::execution::detail::fwd_env(env));
+        }
+    };
+
     template <typename, typename...>
     struct get_signatures;
 
@@ -121,8 +246,7 @@ struct on_t : ::beman::execution::sender_adaptor_closure<on_t> {
     template <typename Sched, typename Child, typename Env>
     struct get_signatures<::beman::execution::detail::basic_sender<::beman::execution::detail::on_t, Sched, Child>,
                           Env> {
-
-        static consteval auto get() noexcept
+        static consteval auto get()
             requires ::std::invocable<::beman::execution::get_start_scheduler_t, Env>
         {
             using transformed_sndr = decltype(on_t::transform_sender(
@@ -141,7 +265,7 @@ struct on_t : ::beman::execution::sender_adaptor_closure<on_t> {
                                                  ::beman::execution::detail::product_type<Sched, Closure>,
                                                  Child>,
         Env> {
-        static constexpr auto get() noexcept
+        static consteval auto get()
             requires ::std::invocable<::beman::execution::get_completion_scheduler_t<::beman::execution::set_value_t>,
                                       ::beman::execution::env_of_t<Child>,
                                       Env>
@@ -157,6 +281,7 @@ struct on_t : ::beman::execution::sender_adaptor_closure<on_t> {
         }
     };
 
+  public:
     template <typename Sender, typename Env>
         requires requires { get_signatures<std::remove_cvref_t<Sender>, Env>::get(); }
     static consteval auto get_completion_signatures() noexcept {
diff --git a/include/beman/execution/detail/starts_on.hpp b/include/beman/execution/detail/starts_on.hpp
index c94dc1a0..c497e4a2 100644
--- a/include/beman/execution/detail/starts_on.hpp
+++ b/include/beman/execution/detail/starts_on.hpp
@@ -30,6 +30,7 @@ import beman.execution.detail.just;
 import beman.execution.detail.let;
 import beman.execution.detail.make_sender;
 import beman.execution.detail.meta.combine;
+import beman.execution.detail.meta.unique;
 import beman.execution.detail.query_with_default;
 import beman.execution.detail.sched_env;
 import beman.execution.detail.schedule_result_t;
@@ -40,7 +41,6 @@ import beman.execution.detail.sends_stopped;
 import beman.execution.detail.set_error;
 import beman.execution.detail.set_stopped;
 import beman.execution.detail.set_value;
-import beman.execution.detail.write_env;
 #else
 #include <beman/execution/detail/basic_sender.hpp>
 #include <beman/execution/detail/completion_signatures.hpp>
@@ -59,6 +59,7 @@ import beman.execution.detail.write_env;
 #include <beman/execution/detail/let.hpp>
 #include <beman/execution/detail/make_sender.hpp>
 #include <beman/execution/detail/meta_combine.hpp>
+#include <beman/execution/detail/meta_unique.hpp>
 #include <beman/execution/detail/sched_env.hpp>
 #include <beman/execution/detail/schedule_result_t.hpp>
 #include <beman/execution/detail/scheduler.hpp>
@@ -67,7 +68,6 @@ import beman.execution.detail.write_env;
 #include <beman/execution/detail/set_error.hpp>
 #include <beman/execution/detail/set_stopped.hpp>
 #include <beman/execution/detail/set_value.hpp>
-#include <beman/execution/detail/write_env.hpp>
 #endif
 
 // ----------------------------------------------------------------------------
@@ -75,7 +75,7 @@ import beman.execution.detail.write_env;
 namespace beman::execution::detail {
 struct starts_on_t {
     template <::beman::execution::detail::sender_for<::beman::execution::detail::starts_on_t> Sender, typename Env>
-    auto transform_sender(::beman::execution::set_value_t, Sender&& sender, const Env&) const noexcept {
+    static auto transform_sender(::beman::execution::set_value_t, Sender&& sender, const Env&) noexcept {
         auto&&         sched{sender.template get<1>()};
         auto&&         child{sender.template get<2>()};
         constexpr bool is_nothrow = ::std::is_nothrow_move_constructible_v<::std::remove_cvref_t<decltype(child)>>;
@@ -95,22 +95,14 @@ struct starts_on_t {
     struct get_signatures<
         ::beman::execution::detail::basic_sender<::beman::execution::detail::starts_on_t, Scheduler, Child>,
         Env> {
-        using scheduler_sender = ::beman::execution::schedule_result_t<Scheduler>;
-        using child_env        = decltype(::beman::execution::detail::join_env(
-            ::beman::execution::detail::sched_env(::std::declval<Scheduler>()),
-            ::beman::execution::detail::fwd_env(::std::declval<Env>())));
-
-        template <typename... E>
-        using as_set_error = ::beman::execution::completion_signatures<::beman::execution::set_error_t(E)...>;
-
-        using value_and_error_types = ::beman::execution::detail::meta::combine<
-            ::beman::execution::completion_signatures_of_t<Child, child_env>,
-            ::beman::execution::error_types_of_t<scheduler_sender, Env, as_set_error>>;
-        using stopped_types =
-            ::std::conditional_t<::beman::execution::sends_stopped<scheduler_sender, Env>,
-                                 ::beman::execution::completion_signatures<::beman::execution::set_stopped_t()>,
-                                 ::beman::execution::completion_signatures<>>;
-        using type = ::beman::execution::detail::meta::combine<value_and_error_types, stopped_types>;
+        static consteval auto get() {
+            using transformed_sndr = decltype(starts_on_t::transform_sender(
+                ::beman::execution::set_value,
+                ::std::declval<::beman::execution::detail::
+                                   basic_sender<::beman::execution::detail::starts_on_t, Scheduler, Child>>(),
+                ::std::declval<Env>()));
+            return ::beman::execution::get_completion_signatures<transformed_sndr, Env>();
+        }
     };
 
     template <typename Scheduler, typename ChildAttrs>
@@ -153,8 +145,8 @@ struct starts_on_t {
 
   public:
     template <typename Sender, typename... Env>
-    static consteval auto get_completion_signatures() noexcept {
-        return typename get_signatures<::std::remove_cvref_t<Sender>, Env...>::type{};
+    static consteval auto get_completion_signatures() {
+        return get_signatures<::std::remove_cvref_t<Sender>, Env...>::get();
     }
 
     struct impls_for : ::beman::execution::detail::default_impls {
diff --git a/tests/beman/execution/exec-inline-scheduler.test.cpp b/tests/beman/execution/exec-inline-scheduler.test.cpp
index 33289808..7a8765e3 100644
--- a/tests/beman/execution/exec-inline-scheduler.test.cpp
+++ b/tests/beman/execution/exec-inline-scheduler.test.cpp
@@ -76,7 +76,8 @@ struct sched_with_domain {
     };
     struct sender {
         using sender_concept = test_std::sender_tag;
-        static consteval auto get_completion_signatures() {
+        template <typename...>
+        static consteval auto get_completion_signatures() noexcept {
             return test_std::completion_signatures<test_std::set_value_t()>();
         }
         template <typename R>
diff --git a/tests/beman/execution/exec-on.test.cpp b/tests/beman/execution/exec-on.test.cpp
index 9b9db35c..60de28d7 100644
--- a/tests/beman/execution/exec-on.test.cpp
+++ b/tests/beman/execution/exec-on.test.cpp
@@ -30,6 +30,47 @@ import beman.execution.detail;
 // ----------------------------------------------------------------------------
 
 namespace {
+struct custom_domain : test_std::default_domain {};
+
+struct custom_scheduler {
+    using scheduler_concept = test_std::scheduler_tag;
+
+    static auto query(test_std::get_forward_progress_guarantee_t) noexcept {
+        return test_std::forward_progress_guarantee::weakly_parallel;
+    }
+
+    static auto query(test_std::get_completion_scheduler_t<test_std::set_value_t>) noexcept -> custom_scheduler {
+        return {};
+    }
+
+    static auto query(test_std::get_completion_domain_t<test_std::set_value_t>) noexcept -> custom_domain {
+        return {};
+    }
+
+    struct env {
+        static auto query(test_std::get_completion_scheduler_t<test_std::set_value_t>) noexcept -> custom_scheduler {
+            return {};
+        }
+    };
+
+    struct sender {
+        using sender_concept = test_std::sender_tag;
+
+        template <typename...>
+        static consteval auto get_completion_signatures() noexcept {
+            return test_std::completion_signatures<test_std::set_value_t()>{};
+        }
+
+        auto connect(auto rcvr) const noexcept { return test_std::connect(test_std::just(), std::move(rcvr)); }
+
+        auto get_env() const noexcept -> env { return {}; }
+    };
+
+    static auto schedule() noexcept { return sender{}; }
+
+    auto operator==(const custom_scheduler&) const -> bool = default;
+};
+
 template <test_std::scheduler Sch, test_std::sender Sndr, test_detail::is_sender_adaptor_closure Closure>
 auto test_interface(Sch sch, Sndr sndr, Closure closure) -> void {
     static_assert(requires {
@@ -48,14 +89,6 @@ auto test_interface(Sch sch, Sndr sndr, Closure closure) -> void {
     test::use(sndr1, sndr2, sndr3);
 }
 
-template <test_detail::sender_for<test_std::on_t> OutSndr>
-auto test_transform_sender(OutSndr out_sndr) -> void {
-    auto s{test_std::on.transform_sender(test_std::set_value, std::move(out_sndr), test_std::env<>{})};
-    static_assert(test_std::sender<decltype(s)>);
-    auto ts{std::move(s) | test_std::then([](auto&&...) {})};
-    static_assert(test_std::sender<decltype(ts)>);
-}
-
 struct on_receiver {
     using receiver_concept = test_std::receiver_tag;
     test::thread_pool& pool;
@@ -68,7 +101,11 @@ static_assert(test_std::receiver<on_receiver>);
 
 auto test_on_attributes() {
     test_std::run_loop loop{};
-    test::sender_env   s{42};
+    static_assert(test_std::dependent_sender<decltype(test_std::on(loop.get_scheduler(), test_std::just()))>);
+
+    test::sender_env s{42};
+    auto             recv_env = test_detail::make_env(test_std::get_start_scheduler, custom_scheduler{});
+
     test::test_sender_env<true>(42, test::test_forwardable_attr{}, s);
     test::test_sender_env<true>(84, test::test_non_forwardable_attr{}, s);
     test::test_sender_env<true>(42, test::test_forwardable_attr{}, test_std::on(loop.get_scheduler(), s));
@@ -77,6 +114,24 @@ auto test_on_attributes() {
         42, test::test_forwardable_attr{}, test_std::on(s, loop.get_scheduler(), test_std::then([]() {})));
     test::test_sender_env<false>(
         84, test::test_non_forwardable_attr{}, test_std::on(s, loop.get_scheduler(), test_std::then([]() {})));
+
+    auto on_sndr1 = test_std::on(loop.get_scheduler(), test_std::just());
+    static_assert(test_std::sender_in<decltype(on_sndr1), decltype(recv_env)>);
+    static_assert(not test_std::sender_in<decltype(on_sndr1), test_std::env<>>);
+
+    auto attrs1 = test_std::get_env(on_sndr1);
+
+    ASSERT(test_std::get_completion_scheduler<test_std::set_value_t>(attrs1, recv_env) == custom_scheduler{});
+
+    static_assert(std::same_as<decltype(test_std::get_completion_domain<test_std::set_value_t>(attrs1, recv_env)),
+                               custom_domain>);
+
+    auto attrs2 = test_std::get_env(
+        test_std::on(test_std::schedule(custom_scheduler{}), loop.get_scheduler(), test_std::then([]() {})));
+    ASSERT(test_std::get_completion_scheduler<test_std::set_value_t>(attrs2, test_std::env<>{}) == custom_scheduler{});
+    static_assert(
+        std::same_as<decltype(test_std::get_completion_domain<test_std::set_value_t>(attrs2, test_std::env<>{})),
+                     custom_domain>);
 }
 } // namespace
 
@@ -88,10 +143,6 @@ TEST(exec_on) {
     static_assert(not test_detail::is_sender_adaptor_closure<decltype(test_std::just([] {}))>);
     test_interface(pool.get_scheduler(), test_std::just(), test_std::then([] {}));
 
-    test_transform_sender(test_detail::make_sender(test_std::on, pool.get_scheduler(), test_std::just()));
-    test_transform_sender(test_detail::make_sender(
-        test_std::on, test_detail::product_type{pool.get_scheduler(), test_std::then([] {})}, test_std::just()));
-
     std::thread::id on_id{};
     std::thread::id pool_id{};
     std::thread::id cont_id{};
diff --git a/tests/beman/execution/exec-parallel-scheduler.test.cpp b/tests/beman/execution/exec-parallel-scheduler.test.cpp
index 4b816b05..5340b29f 100644
--- a/tests/beman/execution/exec-parallel-scheduler.test.cpp
+++ b/tests/beman/execution/exec-parallel-scheduler.test.cpp
@@ -99,6 +99,17 @@ auto test_parallel_scheduler_schedule() -> void {
         test_std::sync_wait(test_std::schedule(sch) | test_std::then([&i]() noexcept { i = 114514; }));
         ASSERT(i == 114514);
     }
+    {
+        static constexpr auto square = [](int i) noexcept { return i * i; };
+        auto                  work = test_std::when_all(test_std::on(sch, test_std::just(0) | test_std::then(square)),
+                                       test_std::on(sch, test_std::just(1) | test_std::then(square)),
+                                       test_std::on(sch, test_std::just(2) | test_std::then(square)));
+
+        if (auto result = test_std::sync_wait(std::move(work))) {
+            auto [i, j, k] = result.value();
+            ASSERT(i == 0 && j == 1 && k == 4);
+        }
+    }
     {
         bool invoked = false;
         test_std::sync_wait(test_std::schedule(sch) |

From ff2a0e2b24d98baea55bac2c63835677f61316bc Mon Sep 17 00:00:00 2001
From: Cra3z <3324654761@qq.com>
Date: Mon, 21 Sep 2026 21:44:09 +0800
Subject: [PATCH 3/5] Add missing headers

---
 include/beman/execution/detail/continues_on.hpp        | 6 +++---
 include/beman/execution/detail/starts_on.hpp           | 2 ++
 tests/beman/execution/exec-parallel-scheduler.test.cpp | 4 ++--
 3 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/include/beman/execution/detail/continues_on.hpp b/include/beman/execution/detail/continues_on.hpp
index 39477c2a..98266d80 100644
--- a/include/beman/execution/detail/continues_on.hpp
+++ b/include/beman/execution/detail/continues_on.hpp
@@ -130,9 +130,9 @@ struct continues_on_t {
         template <typename... E>
         using as_set_error = ::beman::execution::completion_signatures<::beman::execution::set_error_t(E)...>;
         using type         = ::beman::execution::detail::meta::unique<::beman::execution::detail::meta::combine<
-                    decltype(::beman::execution::get_completion_signatures<Sender, Env>()),
-                    ::beman::execution::error_types_of_t<scheduler_sender, Env, as_set_error>,
-                    additional_signatures>>;
+            decltype(::beman::execution::get_completion_signatures<Sender, Env>()),
+            ::beman::execution::error_types_of_t<scheduler_sender, Env, as_set_error>,
+            additional_signatures>>;
     };
 
     template <typename Scheduler, typename ChildAttrs>
diff --git a/include/beman/execution/detail/starts_on.hpp b/include/beman/execution/detail/starts_on.hpp
index c497e4a2..de520929 100644
--- a/include/beman/execution/detail/starts_on.hpp
+++ b/include/beman/execution/detail/starts_on.hpp
@@ -24,6 +24,7 @@ import beman.execution.detail.forward_like;
 import beman.execution.detail.fwd_env;
 import beman.execution.detail.get_completion_domain;
 import beman.execution.detail.get_completion_scheduler;
+import beman.execution.detail.get_completion_signatures;
 import beman.execution.detail.get_env;
 import beman.execution.detail.join_env;
 import beman.execution.detail.just;
@@ -53,6 +54,7 @@ import beman.execution.detail.set_value;
 #include <beman/execution/detail/fwd_env.hpp>
 #include <beman/execution/detail/get_completion_domain.hpp>
 #include <beman/execution/detail/get_completion_scheduler.hpp>
+#include <beman/execution/detail/get_completion_signatures.hpp>
 #include <beman/execution/detail/get_env.hpp>
 #include <beman/execution/detail/join_env.hpp>
 #include <beman/execution/detail/just.hpp>
diff --git a/tests/beman/execution/exec-parallel-scheduler.test.cpp b/tests/beman/execution/exec-parallel-scheduler.test.cpp
index 5340b29f..beb4daf5 100644
--- a/tests/beman/execution/exec-parallel-scheduler.test.cpp
+++ b/tests/beman/execution/exec-parallel-scheduler.test.cpp
@@ -102,8 +102,8 @@ auto test_parallel_scheduler_schedule() -> void {
     {
         static constexpr auto square = [](int i) noexcept { return i * i; };
         auto                  work = test_std::when_all(test_std::on(sch, test_std::just(0) | test_std::then(square)),
-                                       test_std::on(sch, test_std::just(1) | test_std::then(square)),
-                                       test_std::on(sch, test_std::just(2) | test_std::then(square)));
+                                                        test_std::on(sch, test_std::just(1) | test_std::then(square)),
+                                                        test_std::on(sch, test_std::just(2) | test_std::then(square)));
 
         if (auto result = test_std::sync_wait(std::move(work))) {
             auto [i, j, k] = result.value();

From d53fe641858d8058b234d5dcfa589f0457f503c5 Mon Sep 17 00:00:00 2001
From: Cra3z <CrazyCra3z@outlook.com>
Date: Tue, 22 Sep 2026 13:55:25 +0800
Subject: [PATCH 4/5] gcc 15 workaround

---
 examples/intro_1_hello_world.cpp            | 2 --
 examples/intro_2_hello_async.cpp            | 2 --
 examples/playground.cpp                     | 2 --
 examples/sender_demo.cpp                    | 2 --
 examples/when_all_cancel.cpp                | 2 --
 include/beman/execution/detail/when_all.hpp | 3 ++-
 6 files changed, 2 insertions(+), 11 deletions(-)

diff --git a/examples/intro_1_hello_world.cpp b/examples/intro_1_hello_world.cpp
index 0dd16121..5a427a70 100644
--- a/examples/intro_1_hello_world.cpp
+++ b/examples/intro_1_hello_world.cpp
@@ -25,7 +25,6 @@ using namespace std::string_literals;
 
 int main() {
     // clang-format off
-#if !defined(__GNUC__) || defined(__clang__) || (__GNUC__ > 15) || !defined(BEMAN_HAS_MODULES)
     auto [result] =
     ex::sync_wait(
         ex::when_all(
@@ -34,7 +33,6 @@ int main() {
         ) | ex::then([](auto const& s1, auto const& s2) { return s1 + s2; })
         ).value_or(std::tuple(""s))
         ;
-#endif
     // clang-format on
 
     // std::cout << std::get<0>(v) << '\n';
diff --git a/examples/intro_2_hello_async.cpp b/examples/intro_2_hello_async.cpp
index 4ff53c6b..d46041b0 100644
--- a/examples/intro_2_hello_async.cpp
+++ b/examples/intro_2_hello_async.cpp
@@ -28,7 +28,6 @@ using namespace std::chrono_literals;
 
 int main() {
     std::cout << std::unitbuf;
-#if !defined(__GNUC__) || defined(__clang__) || (__GNUC__ > 15) || !defined(BEMAN_HAS_MODULES)
     intro::timer timer;
 
     // clang-format off
@@ -48,5 +47,4 @@ int main() {
     // clang-format on
 
     std::cout << result << "\n";
-#endif
 }
diff --git a/examples/playground.cpp b/examples/playground.cpp
index 186e1fff..0bfe0709 100644
--- a/examples/playground.cpp
+++ b/examples/playground.cpp
@@ -21,10 +21,8 @@ namespace ex = ::beman::execution;
 // ----------------------------------------------------------------------------
 
 int main() {
-#if !defined(__GNUC__) || defined(__clang__) || (__GNUC__ > 15) || !defined(BEMAN_HAS_MODULES)
     auto [result] = ex::sync_wait(ex::when_all(ex::just(std::string("hello, ")), ex::just(std::string("world"))) |
                                   ex::then([](const auto& s1, const auto& s2) { return s1 + s2; }))
                         .value_or(std::tuple(std::string("oops")));
     std::cout << "result='" << result << "'\n";
-#endif
 }
diff --git a/examples/sender_demo.cpp b/examples/sender_demo.cpp
index aa1ff8f9..255b8560 100644
--- a/examples/sender_demo.cpp
+++ b/examples/sender_demo.cpp
@@ -72,14 +72,12 @@ int main() {
             ex::write_env(std::move(w), ex::detail::make_env(ex::get_allocator, std::pmr::polymorphic_allocator<>()));
 
         std::cout << "before start\n";
-#if !defined(__GNUC__) || defined(__clang__) || (__GNUC__ > 15) || !defined(BEMAN_HAS_MODULES)
         auto r = ex::sync_wait(std::move(e));
         if (r) {
             auto [v] = *r;
             std::cout << "produced='" << v << "'\n";
         } else
             std::cout << "operation was cancelled\n";
-#endif
         std::cout << "after start\n";
     } catch (const std::exception& ex) {
         std::cout << "ERROR: " << ex.what() << "\n";
diff --git a/examples/when_all_cancel.cpp b/examples/when_all_cancel.cpp
index cba9096f..f107d7a9 100644
--- a/examples/when_all_cancel.cpp
+++ b/examples/when_all_cancel.cpp
@@ -150,7 +150,6 @@ eager(Sender&&) -> eager<std::remove_cvref_t<Sender>>;
 } // namespace
 
 auto main() -> int {
-#if !defined(__GNUC__) || defined(__clang__) || (__GNUC__ > 15) || !defined(BEMAN_HAS_MODULES)
     auto s{eager{ex::when_all(await_stop{})}};
 
     ex::inplace_stop_source source{};
@@ -160,5 +159,4 @@ auto main() -> int {
     std::cout << "started\n";
     source.request_stop();
     std::cout << "done\n";
-#endif
 }
diff --git a/include/beman/execution/detail/when_all.hpp b/include/beman/execution/detail/when_all.hpp
index c7323415..03c2ee1d 100644
--- a/include/beman/execution/detail/when_all.hpp
+++ b/include/beman/execution/detail/when_all.hpp
@@ -241,6 +241,8 @@ struct when_all_t {
         };
         static constexpr auto get_env{get_env_impl{}};
 
+        struct nonesuch {};
+
         enum class disposition : unsigned char { started, error, stopped };
 
         template <typename... Values>
@@ -249,7 +251,6 @@ struct when_all_t {
 
         template <typename Receiver, typename... Sender>
         struct state_type {
-            struct nonesuch {};
             using env_t     = when_all_env<::beman::execution::env_of_t<Receiver>>;
             using copy_fail = ::std::conditional_t<
                 (... && ::beman::execution::value_types_of_t<Sender,

From 4a2d80c6ceda692ba265147cd37780e0b590293b Mon Sep 17 00:00:00 2001
From: Cra3z <CrazyCra3z@outlook.com>
Date: Tue, 22 Sep 2026 18:11:24 +0800
Subject: [PATCH 5/5] Refactor `continues_on`

---
 include/beman/execution/detail/continues_on.hpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/beman/execution/detail/continues_on.hpp b/include/beman/execution/detail/continues_on.hpp
index 98266d80..c5105e04 100644
--- a/include/beman/execution/detail/continues_on.hpp
+++ b/include/beman/execution/detail/continues_on.hpp
@@ -123,7 +123,7 @@ struct continues_on_t {
         Env> {
         using scheduler_sender      = ::beman::execution::schedule_result_t<Scheduler>;
         using additional_signatures = ::std::conditional_t<
-            ::beman::execution::sends_stopped<scheduler_sender>,
+            ::beman::execution::sends_stopped<scheduler_sender, Env>,
             ::beman::execution::completion_signatures<::beman::execution::set_error_t(::std::exception_ptr),
                                                       ::beman::execution::set_stopped_t()>,
             ::beman::execution::completion_signatures<::beman::execution::set_error_t(::std::exception_ptr)>>;