Use standard placeholders for implementing asio::placeholders.

Adds compatibility with both std::bind and boost::bind.

include/boost/asio/placeholders.hpp

@@ -16,10 +16,7 @@
 #endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
 
 #include <boost/asio/detail/config.hpp>
-
-#if defined(BOOST_ASIO_HAS_BOOST_BIND)
-# include <boost/bind/arg.hpp>
-#endif // defined(BOOST_ASIO_HAS_BOOST_BIND)
+#include <boost/asio/detail/functional.hpp>
 
 #include <boost/asio/detail/push_options.hpp>
 
@@ -29,119 +26,46 @@ namespace placeholders {
 
 #if defined(GENERATING_DOCUMENTATION)
 
-/// An argument placeholder, for use with boost::bind(), that corresponds to
-/// the error argument of a handler for any of the asynchronous functions.
+/// An argument placeholder, for use with std::bind() or boost::bind(), that
+/// corresponds to the error argument of a handler for any of the asynchronous
+/// functions.
 unspecified error;
 
-/// An argument placeholder, for use with boost::bind(), that corresponds to
-/// the bytes_transferred argument of a handler for asynchronous functions such
-/// as boost::asio::basic_stream_socket::async_write_some or
+/// An argument placeholder, for use with std::bind() or boost::bind(), that
+/// corresponds to the bytes_transferred argument of a handler for asynchronous
+/// functions such as boost::asio::basic_stream_socket::async_write_some or
 /// boost::asio::async_write.
 unspecified bytes_transferred;
 
-/// An argument placeholder, for use with boost::bind(), that corresponds to
-/// the iterator argument of a handler for asynchronous functions such as
-/// boost::asio::async_connect.
+/// An argument placeholder, for use with std::bind() or boost::bind(), that
+/// corresponds to the iterator argument of a handler for asynchronous functions
+/// such as boost::asio::async_connect.
 unspecified iterator;
 
-/// An argument placeholder, for use with boost::bind(), that corresponds to
-/// the results argument of a handler for asynchronous functions such as
-/// boost::asio::basic_resolver::async_resolve.
+/// An argument placeholder, for use with std::bind() or boost::bind(), that
+/// corresponds to the results argument of a handler for asynchronous functions
+/// such as boost::asio::basic_resolver::async_resolve.
 unspecified results;
 
-/// An argument placeholder, for use with boost::bind(), that corresponds to
-/// the results argument of a handler for asynchronous functions such as
-/// boost::asio::async_connect.
+/// An argument placeholder, for use with std::bind() or boost::bind(), that
+/// corresponds to the results argument of a handler for asynchronous functions
+/// such as boost::asio::async_connect.
 unspecified endpoint;
 
-/// An argument placeholder, for use with boost::bind(), that corresponds to
-/// the signal_number argument of a handler for asynchronous functions such as
-/// boost::asio::signal_set::async_wait.
+/// An argument placeholder, for use with std::bind() or boost::bind(), that
+/// corresponds to the signal_number argument of a handler for asynchronous
+/// functions such as boost::asio::signal_set::async_wait.
 unspecified signal_number;
 
-#elif defined(BOOST_ASIO_HAS_BOOST_BIND)
-# if defined(__BORLANDC__) || defined(__GNUC__)
-
-inline boost::arg<1> error()
-{
-  return boost::arg<1>();
-}
-
-inline boost::arg<2> bytes_transferred()
-{
-  return boost::arg<2>();
-}
-
-inline boost::arg<2> iterator()
-{
-  return boost::arg<2>();
-}
-
-inline boost::arg<2> results()
-{
-  return boost::arg<2>();
-}
-
-inline boost::arg<2> endpoint()
-{
-  return boost::arg<2>();
-}
-
-inline boost::arg<2> signal_number()
-{
-  return boost::arg<2>();
-}
-
-# else
-
-namespace detail
-{
-  template <int Number>
-  struct placeholder
-  {
-    static boost::arg<Number>& get()
-    {
-      static boost::arg<Number> result;
-      return result;
-    }
-  };
-}
-
-#  if defined(BOOST_ASIO_MSVC) && (BOOST_ASIO_MSVC < 1400)
-
-static boost::arg<1>& error
-  = boost::asio::placeholders::detail::placeholder<1>::get();
-static boost::arg<2>& bytes_transferred
-  = boost::asio::placeholders::detail::placeholder<2>::get();
-static boost::arg<2>& iterator
-  = boost::asio::placeholders::detail::placeholder<2>::get();
-static boost::arg<2>& results
-  = boost::asio::placeholders::detail::placeholder<2>::get();
-static boost::arg<2>& endpoint
-  = boost::asio::placeholders::detail::placeholder<2>::get();
-static boost::arg<2>& signal_number
-  = boost::asio::placeholders::detail::placeholder<2>::get();
-
-#  else
-
-namespace
-{
-  boost::arg<1>& error
-    = boost::asio::placeholders::detail::placeholder<1>::get();
-  boost::arg<2>& bytes_transferred
-    = boost::asio::placeholders::detail::placeholder<2>::get();
-  boost::arg<2>& iterator
-    = boost::asio::placeholders::detail::placeholder<2>::get();
-  boost::arg<2>& results
-    = boost::asio::placeholders::detail::placeholder<2>::get();
-  boost::arg<2>& endpoint
-    = boost::asio::placeholders::detail::placeholder<2>::get();
-  boost::arg<2>& signal_number
-    = boost::asio::placeholders::detail::placeholder<2>::get();
-} // namespace
-
-#  endif
-# endif
+#else
+
+static constexpr auto& error = std::placeholders::_1;
+static constexpr auto& bytes_transferred = std::placeholders::_2;
+static constexpr auto& iterator = std::placeholders::_2;
+static constexpr auto& results = std::placeholders::_2;
+static constexpr auto& endpoint = std::placeholders::_2;
+static constexpr auto& signal_number = std::placeholders::_2;
+
 #endif
 
 } // namespace placeholders