Simplify some type trait expressions

fix #466

example/http/server/fast/http_server_fast.cpp

@@ -88,7 +88,8 @@ public:
 
 private:
     using alloc_t = fields_alloc<char>;
-    using request_body_t = http::basic_dynamic_body<boost::beast::flat_static_buffer<1024 * 1024>>;
+    //using request_body_t = http::basic_dynamic_body<boost::beast::flat_static_buffer<1024 * 1024>>;
+    using request_body_t = http::string_body;
 
     // The acceptor used to listen for incoming connections.
     tcp::acceptor& acceptor_;

include/boost/beast/core/detail/type_traits.hpp

@@ -162,8 +162,7 @@ template<class T, class E>
 struct is_contiguous_container<T, E, void_t<
     decltype(
         std::declval<std::size_t&>() = std::declval<T const&>().size(),
-        std::declval<E*&>() = std::declval<T&>().data(),
+        std::declval<E*&>() = std::declval<T&>().data()),
-        (void)0),
     typename std::enable_if<
         std::is_same<
             typename std::remove_cv<E>::type,

include/boost/beast/core/type_traits.hpp

@@ -118,8 +118,7 @@ struct has_get_executor : std::false_type {};
 
 template<class T>
 struct has_get_executor<T, beast::detail::void_t<decltype(
-        std::declval<T&>().get_executor(),
+        std::declval<T&>().get_executor())>> : std::true_type {};
-    (void)0)>> : std::true_type {};
 #endif
 
 /** Alias for `T::lowest_layer_type` if it exists, else `T`
@@ -195,8 +194,8 @@ template<class T>
 struct is_async_read_stream<T, detail::void_t<decltype(
     std::declval<T>().async_read_some(
         std::declval<detail::MutableBufferSequence>(),
-        std::declval<detail::ReadHandler>()),
+        std::declval<detail::ReadHandler>())
-            (void)0)>> : std::integral_constant<bool,
+            )>> : std::integral_constant<bool,
     has_get_executor<T>::value
         > {};
 #endif
@@ -239,8 +238,8 @@ template<class T>
 struct is_async_write_stream<T, detail::void_t<decltype(
     std::declval<T>().async_write_some(
         std::declval<detail::ConstBufferSequence>(),
-        std::declval<detail::WriteHandler>()),
+        std::declval<detail::WriteHandler>())
-            (void)0)>> : std::integral_constant<bool,
+            )>> : std::integral_constant<bool,
     has_get_executor<T>::value
         > {};
 #endif
@@ -285,8 +284,8 @@ struct is_sync_read_stream<T, detail::void_t<decltype(
         std::declval<detail::MutableBufferSequence>()),
     std::declval<std::size_t&>() = std::declval<T>().read_some(
         std::declval<detail::MutableBufferSequence>(),
-        std::declval<boost::system::error_code&>()),
+        std::declval<boost::system::error_code&>())
-            (void)0)>> : std::true_type {};
+            )>> : std::true_type {};
 #endif
 
 /** Determine if `T` meets the requirements of @b SyncWriteStream.
@@ -329,8 +328,8 @@ struct is_sync_write_stream<T, detail::void_t<decltype(
         std::declval<detail::ConstBufferSequence>()),
     std::declval<std::size_t&>() = std::declval<T&>().write_some(
         std::declval<detail::ConstBufferSequence>(),
-        std::declval<boost::system::error_code&>()),
+        std::declval<boost::system::error_code&>())
-            (void)0)>> : std::true_type {};
+            )>> : std::true_type {};
 #endif
 
 /** Determine if `T` meets the requirements of @b AsyncStream.
@@ -467,8 +466,8 @@ struct is_file<T, detail::void_t<decltype(
     std::declval<std::size_t&>() = std::declval<T&>().write(
         std::declval<void const*>(),
         std::declval<std::size_t>(),
-        std::declval<error_code&>()),
+        std::declval<error_code&>())
-            (void)0)>> : std::integral_constant<bool,
+            )>> : std::integral_constant<bool,
     std::is_default_constructible<T>::value &&
     std::is_destructible<T>::value
         > {};

include/boost/beast/http/detail/chunk_encode.hpp

@@ -57,8 +57,8 @@ struct is_chunk_extensions : std::false_type {};
 
 template<class T>
 struct is_chunk_extensions<T, beast::detail::void_t<decltype(
-    std::declval<string_view&>() = std::declval<T&>().str(),
+    std::declval<string_view&>() = std::declval<T&>().str()
-        (void)0)>> : std::true_type
+        )>> : std::true_type
 {
 };
 

include/boost/beast/http/detail/type_traits.hpp

@@ -93,8 +93,8 @@ struct is_body_sized<T, beast::detail::void_t<
     typename T::value_type,
         decltype(
     std::declval<std::uint64_t&>() =
-        T::size(std::declval<typename T::value_type const&>()),
+        T::size(std::declval<typename T::value_type const&>())
-    (void)0)>> : std::true_type {};
+    )>> : std::true_type {};
 
 template<class T>
 struct is_fields_helper : T

include/boost/beast/http/type_traits.hpp

@@ -86,8 +86,8 @@ struct is_body_writer<T, beast::detail::void_t<
     std::declval<typename T::writer&>().init(std::declval<error_code&>()),
     std::declval<boost::optional<std::pair<
             typename T::writer::const_buffers_type, bool>>&>() =
-            std::declval<typename T::writer>().get(std::declval<error_code&>()),
+            std::declval<typename T::writer>().get(std::declval<error_code&>())
-        (void)0)>> : std::integral_constant<bool,
+        )>> : std::integral_constant<bool,
     boost::asio::is_const_buffer_sequence<
         typename T::writer::const_buffers_type>::value && (
     (std::is_constructible<typename T::writer,
@@ -142,8 +142,8 @@ struct is_body_reader<T, beast::detail::void_t<decltype(
             std::declval<boost::asio::const_buffer>(),
             std::declval<error_code&>()),
     std::declval<typename T::reader&>().finish(
-        std::declval<error_code&>()),
+        std::declval<error_code&>())
-    (void)0)>> : std::integral_constant<bool,
+    )>> : std::integral_constant<bool,
         (std::is_constructible<typename T::reader,
             header<true, detail::fields_model>&,
                 typename T::value_type&>::value &&