From a707db8193b30b6cc4a3d10ee946f7f245e07097 Mon Sep 17 00:00:00 2001

From: Christopher Kohlhoff <chris@kohlhoff.com>

Date: Tue, 7 Apr 2020 11:18:31 +1000

Subject: [PATCH] Support C++20 concept syntax.

---

 include/boost/asio/async_result.hpp  | 18 +++++++++++-------

 include/boost/asio/detail/config.hpp | 10 +++++++---

 2 files changed, 18 insertions(+), 10 deletions(-)

diff --git a/include/boost/asio/async_result.hpp b/include/boost/asio/async_result.hpp

index 2f4b337d1..0eea0f471 100644

--- boost/asio/async_result.hpp

+++ boost/asio/async_result.hpp

@@ -66,9 +66,10 @@ BOOST_ASIO_CONCEPT completion_signature =

 #define BOOST_ASIO_COMPLETION_SIGNATURE \

   ::boost::asio::completion_signature

-template <typename T, completion_signature Signature>

+template <typename T, typename Signature>

 BOOST_ASIO_CONCEPT completion_handler_for =

-  detail::is_completion_handler_for<T, Signature>::value;

+  detail::is_completion_signature<Signature>::value

+    && detail::is_completion_handler_for<T, Signature>::value;

 #define BOOST_ASIO_COMPLETION_HANDLER_FOR(s) \

   ::boost::asio::completion_handler_for<s>

@@ -488,11 +489,14 @@ struct initiation_archetype

 } // namespace detail

-template <typename T, completion_signature Signature>

-BOOST_ASIO_CONCEPT completion_token_for = requires(T&& t)

-{

-  async_initiate<T, Signature>(detail::initiation_archetype<Signature>{}, t);

-};

+template <typename T, typename Signature>

+BOOST_ASIO_CONCEPT completion_token_for =

+  detail::is_completion_signature<Signature>::value

+  &&

+  requires(T&& t)

+  {

+    async_initiate<T, Signature>(detail::initiation_archetype<Signature>{}, t);

+  };

 #define BOOST_ASIO_COMPLETION_TOKEN_FOR(s) \

   ::boost::asio::completion_token_for<s>

diff --git a/include/boost/asio/detail/config.hpp b/include/boost/asio/detail/config.hpp

index 27d1d6753..6b85cccea 100644

--- boost/asio/detail/config.hpp

+++ boost/asio/detail/config.hpp

@@ -343,10 +343,14 @@

 // Support concepts on compilers known to allow them.

 #if !defined(BOOST_ASIO_HAS_CONCEPTS)

 # if !defined(BOOST_ASIO_DISABLE_CONCEPTS)

-#  if __cpp_concepts

+#  if defined(__cpp_concepts)

 #   define BOOST_ASIO_HAS_CONCEPTS 1

-#   define BOOST_ASIO_CONCEPT concept bool

-#  endif // __cpp_concepts

+#   if (__cpp_concepts >= 201707)

+#    define BOOST_ASIO_CONCEPT concept

+#   else // (__cpp_concepts >= 201707)

+#    define BOOST_ASIO_CONCEPT concept bool

+#   endif // (__cpp_concepts >= 201707)

+#  endif // defined(__cpp_concepts)

 # endif // !defined(BOOST_ASIO_DISABLE_CONCEPTS)

 #endif // !defined(BOOST_ASIO_HAS_CONCEPTS)