Simplify exit_scope_sender_of_t

include/beman/execution/detail/enter_scope_sender_in.hpp

@@ -7,18 +7,19 @@
 #include <beman/execution/detail/common.hpp>
 #ifdef BEMAN_HAS_MODULES
 import beman.execution.detail.enter_scope_sender;
+import beman.execution.detail.env;
 import beman.execution.detail.exit_scope_sender_of_t;
 import beman.execution.detail.sender_in;
 #else
 #include <beman/execution/detail/enter_scope_sender.hpp>
+#include <beman/execution/detail/env.hpp>
 #include <beman/execution/detail/exit_scope_sender_of_t.hpp>
 #include <beman/execution/detail/sender_in.hpp>
 #endif
 
 // ----------------------------------------------------------------------------
 
 namespace beman::execution {
-template <typename Sender, typename... Env>
 /*!
  * \brief An enter scope sender that can operate in the environment `Env...`.
  * \headerfile beman/execution/execution.hpp <beman/execution/execution.hpp>
@@ -31,9 +32,10 @@ template <typename Sender, typename... Env>
  *     signature is unary, and the type of the value models `exit_sender_in<Env...>`.
  *   - Semantic: The above exit sender undoes the action of the enter scope sender which sent it.
  */
+template <typename Sender, typename Env = ::beman::execution::env<>>
 concept enter_scope_sender_in =
-    ::beman::execution::enter_scope_sender<Sender> && ::beman::execution::sender_in<Sender, Env...> &&
-    requires { typename ::beman::execution::exit_scope_sender_of_t<Sender, Env...>; };
+    ::beman::execution::enter_scope_sender<Sender> && ::beman::execution::sender_in<Sender, Env> &&
+    requires { typename ::beman::execution::exit_scope_sender_of_t<Sender, Env>; };
 } // namespace beman::execution
 
 // ----------------------------------------------------------------------------

include/beman/execution/detail/exit_scope_sender_of_t.hpp

@@ -12,61 +12,20 @@ import std;
 #include <type_traits>
 #endif
 #ifdef BEMAN_HAS_MODULES
-import beman.execution.detail.completion_signatures_of_t;
-import beman.execution.detail.completion_signatures;
 import beman.execution.detail.enter_scope_sender;
+import beman.execution.detail.env;
 import beman.execution.detail.exit_scope_sender_in;
-import beman.execution.detail.set_value;
+import beman.execution.detail.single_sender_value_type;
 #else
-#include <beman/execution/detail/completion_signatures_of_t.hpp>
-#include <beman/execution/detail/completion_signatures.hpp>
 #include <beman/execution/detail/enter_scope_sender.hpp>
+#include <beman/execution/detail/env.hpp>
 #include <beman/execution/detail/exit_scope_sender_in.hpp>
-#include <beman/execution/detail/set_value.hpp>
+#include <beman/execution/detail/single_sender_value_type.hpp>
 #endif
 
 // ----------------------------------------------------------------------------
 
 namespace beman::execution {
-
-namespace detail {
-
-/// `true` if `Sig` is a value completion signature, i.e. `set_value_t(Args...)`.
-template <typename Sig>
-inline constexpr bool is_value_completion_sig = false;
-template <typename... Args>
-inline constexpr bool is_value_completion_sig<::beman::execution::set_value_t(Args...)> = true;
-
-/// Finds the type T from the unique unary set_value_t(T) in a signature list.
-/// Not defined (substitution failure) if there are zero or two or more value signatures,
-/// or if the sole value signature is not unary.
-template <typename... Sigs>
-struct single_value_sender;
-
-template <typename T, typename... Rest>
-    requires(!(::beman::execution::detail::is_value_completion_sig<Rest> || ...))
-struct single_value_sender<::beman::execution::set_value_t(T), Rest...> {
-    using type = T;
-};
-
-template <typename First, typename... Rest>
-    requires(!::beman::execution::detail::is_value_completion_sig<First>)
-struct single_value_sender<First, Rest...> : ::beman::execution::detail::single_value_sender<Rest...> {};
-
-/// Helper that extracts the exit scope sender type from a list of completion signatures.
-template <typename Signatures, typename... Env>
-struct extract_exit_scope_sender;
-
-template <typename... Sigs, typename... Env>
-    requires requires { typename ::beman::execution::detail::single_value_sender<Sigs...>::type; } &&
-             ::beman::execution::
-                 exit_scope_sender_in<typename ::beman::execution::detail::single_value_sender<Sigs...>::type, Env...>
-struct extract_exit_scope_sender<::beman::execution::completion_signatures<Sigs...>, Env...> {
-    using type = typename ::beman::execution::detail::single_value_sender<Sigs...>::type;
-};
-
-} // namespace detail
-
 /*!
  * \brief Represents the type of exit scope sender which an asynchronous operation formed from
  *        `Sender` in `Env...` yield on completion.
@@ -77,9 +36,10 @@ struct extract_exit_scope_sender<::beman::execution::completion_signatures<Sigs.
  * If there is no value completion signature, or if there are two or more value completion signatures, this type is not
  * defined.
  */
-template <::beman::execution::enter_scope_sender Sender, typename... Env>
-using exit_scope_sender_of_t = typename ::beman::execution::detail::
-    extract_exit_scope_sender<::beman::execution::completion_signatures_of_t<Sender, Env...>, Env...>::type;
+template <::beman::execution::enter_scope_sender Sender, typename Env = ::beman::execution::env<>>
+    requires ::beman::execution::
+                 exit_scope_sender_in<::beman::execution::detail::single_sender_value_type<Sender, Env>, Env>
+using exit_scope_sender_of_t = ::beman::execution::detail::single_sender_value_type<Sender, Env>;
 } // namespace beman::execution
 
 // ----------------------------------------------------------------------------

tests/beman/execution/exec-scope-snd-concepts.test.cpp

@@ -81,6 +81,4 @@ TEST(exec_scope_snd_concepts) {
 
     using t5 = sender<test_std::set_value_t(int), test_std::set_error_t(int), test_std::set_stopped_t()>;
     static_assert(!test_std::enter_scope_sender_in<t5, test_std::env<>>);
-
-    // TODO: use sender<...>
 }