address issue 200: use stop_callback_traits to support std::stop_token

include/beman/execution/detail/stop_callback_for_t.hpp

@@ -4,13 +4,15 @@
 #ifndef INCLUDED_BEMAN_EXECUTION_DETAIL_STOP_CALLBACK_FOR
 #define INCLUDED_BEMAN_EXECUTION_DETAIL_STOP_CALLBACK_FOR
 
+#include <beman/execution/detail/stop_token_traits.hpp>
 #include <concepts>
 
 // ----------------------------------------------------------------------------
 
 namespace beman::execution {
 template <class Token, class CallbackFun>
-using stop_callback_for_t = typename Token::template callback_type<CallbackFun>;
+using stop_callback_for_t =
+    typename ::beman::execution::detail::stoppable_token_traits<Token>::template callback_type<CallbackFun>;
 }
 
 namespace beman::execution::detail {

include/beman/execution/detail/stop_token_traits.hpp

@@ -0,0 +1,32 @@
+// include/beman/execution/detail/stop_token_traits.hpp               -*-C++-*-
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+#ifndef INCLUDED_BEMAN_EXECUTION_DETAIL_STOP_TOKEN_TRAITS
+#define INCLUDED_BEMAN_EXECUTION_DETAIL_STOP_TOKEN_TRAITS
+
+#include <beman/execution/detail/check_type_alias_exist.hpp>
+#include <stop_token>
+
+// ----------------------------------------------------------------------------
+
+namespace beman::execution::detail {
+template <typename>
+struct stoppable_token_traits;
+
+template <typename Token>
+    requires requires { typename check_type_alias_exist<Token::template callback_type>; }
+struct stoppable_token_traits<Token> {
+    template <typename Fn>
+    using callback_type = typename Token::template callback_type<Fn>;
+};
+
+template <>
+struct stoppable_token_traits<std::stop_token> {
+    template <typename Fn>
+    using callback_type = std::stop_callback<Fn>;
+};
+} // namespace beman::execution::detail
+
+// ----------------------------------------------------------------------------
+
+#endif

include/beman/execution/detail/stoppable_token.hpp

@@ -5,14 +5,16 @@
 #define INCLUDED_BEMAN_EXECUTION_DETAIL_STOPPABLE_TOKEN
 
 #include <beman/execution/detail/check_type_alias_exist.hpp>
+#include <beman/execution/detail/stop_token_traits.hpp>
 #include <concepts>
 
 // ----------------------------------------------------------------------------
 
 namespace beman::execution {
 template <typename Token>
 concept stoppable_token = requires(const Token& token) {
-    typename ::beman::execution::detail::check_type_alias_exist<Token::template callback_type>;
+    typename ::beman::execution::detail::check_type_alias_exist<
+        ::beman::execution::detail::stoppable_token_traits<Token>::template callback_type>;
     { token.stop_requested() } noexcept -> ::std::same_as<bool>;
     { token.stop_possible() } noexcept -> ::std::same_as<bool>;
     { Token(token) } noexcept;

tests/beman/execution/CMakeLists.txt

@@ -21,6 +21,7 @@ endif()
 list(
     APPEND execution_tests
     exec-affine-on.test
+    issue-200.test
     issue-174.test
     issue-186.test
     exec-scope-counting.test

tests/beman/execution/issue-200.test.cpp

@@ -0,0 +1,13 @@
+// tests/beman/execution/issue-200.test.cpp                           -*-C++-*-
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+#include <beman/execution/detail/stoppable_token.hpp>
+#include <test/execution.hpp>
+#include <stop_token>
+
+// ----------------------------------------------------------------------------
+
+auto main() -> int {
+    static_assert(test_std::stoppable_token<std::stop_token>);
+    return 0;
+}