Scope Senders & Asynchronous Objects

include/exec/enter_scope_sender.hpp

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+/*
+ * SPDX-FileCopyrightText: Copyright (c) 2025 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
+ *                         Copyright (c) 2025 Robert Leahy. All rights reserved.
+ * SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+ *
+ * Licensed under the Apache License, Version 2.0 with LLVM Exceptions (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * https://llvm.org/LICENSE.txt
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#pragma once
+
+#include <concepts>
+#include <type_traits>
+#include <utility>
+
+#include "exit_scope_sender.hpp"
+#include "../stdexec/execution.hpp"
+
+namespace exec {
+
+template<typename Sender>
+concept enter_scope_sender = ::STDEXEC::sender<Sender>;
+
+namespace detail::exit_scope_sender_of {
+
+template<typename Env, typename... Args>
+struct transform_set_value_impl;
+template<typename Env, ::exec::exit_scope_sender_in<Env> Sender>
+struct transform_set_value_impl<Env, Sender> {
+  using type = ::STDEXEC::completion_signatures<
+    ::STDEXEC::set_value_t(Sender)>;
+};
+
+template<typename Env>
+struct transform_set_value {
+  template<typename... Args>
+  using fn = transform_set_value_impl<Env, Args...>::type;
+};
+
+template<typename T>
+using transform_set_error = ::STDEXEC::completion_signatures<>;
+
+template<typename Signatures>
+struct impl;
+template<typename Sender>
+struct impl<
+  ::STDEXEC::completion_signatures<
+    ::STDEXEC::set_value_t(Sender)>>
+{
+  using type = Sender;
+};
+
+}
+
+template<enter_scope_sender Constructor, typename Env>
+using exit_scope_sender_of_t = detail::exit_scope_sender_of::impl<
+  ::STDEXEC::transform_completion_signatures<
+    ::STDEXEC::completion_signatures_of_t<Constructor, Env>,
+    ::STDEXEC::completion_signatures<>,
+    detail::exit_scope_sender_of::transform_set_value<Env>::template fn,
+    detail::exit_scope_sender_of::transform_set_error,
+    ::STDEXEC::completion_signatures<>>>::type;
+
+template<typename Sender, typename Env>
+concept enter_scope_sender_in =
+  enter_scope_sender<Sender> &&
+  ::STDEXEC::sender_in<Sender, Env> &&
+  requires {
+    typename exit_scope_sender_of_t<Sender, Env>;
+  };
+
+}  // namespace exec