Tidy up and make get_lowest_layer public

fix #379

include/beast/core/buffered_read_stream.hpp

@@ -108,12 +108,7 @@ public:
 
     /// The type of the lowest layer.
     using lowest_layer_type =
-#if BEAST_DOXYGEN
-        implementation_defined;
-#else
-        typename detail::get_lowest_layer<
-            next_layer_type>::type;
-#endif
+        typename get_lowest_layer<next_layer_type>::type;
 
     /** Move constructor.
 

include/beast/core/detail/get_lowest_layer.hpp

@@ -1,20 +0,0 @@
-//
-// Copyright (c) 2013-2017 Vinnie Falco (vinnie dot falco at gmail dot com)
-//
-// Distributed under the Boost Software License, Version 1.0. (See accompanying
-// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
-//
-
-#ifndef BEAST_DETAIL_GET_LOWEST_LAYER_HPP
-#define BEAST_DETAIL_GET_LOWEST_LAYER_HPP
-
-#include <type_traits>
-
-namespace beast {
-namespace detail {
-
-
-} // detail
-} // beast
-
-#endif

include/beast/core/detail/type_traits.hpp

@@ -122,39 +122,6 @@ struct is_invocable<C, R(A...)>
 };
 /** @} */
 
-template<class T>
-class has_lowest_layer
-{
-    template<class U, class R =
-        typename U::lowest_layer_type>
-    static std::true_type check(int);
-    template<class>
-    static std::false_type check(...);
-    using type = decltype(check<T>(0));
-public:
-    static bool constexpr value = type::value;
-};
-
-template<class T, bool B>
-struct maybe_get_lowest_layer
-{
-    using type = T;
-};
-
-template<class T>
-struct maybe_get_lowest_layer<T, true>
-{
-    using type = typename T::lowest_layer_type;
-};
-
-// Returns T::lowest_layer_type if it exists, else T
-template<class T>
-struct get_lowest_layer
-{
-    using type = typename maybe_get_lowest_layer<T,
-        has_lowest_layer<T>::value>::type;
-};
-
 //------------------------------------------------------------------------------
 
 //

include/beast/core/type_traits.hpp

@@ -15,6 +15,12 @@
 
 namespace beast {
 
+//------------------------------------------------------------------------------
+//
+// Buffer concepts
+//
+//------------------------------------------------------------------------------
+
 /// Determine if `T` meets the requirements of @b ConstBufferSequence.
 template<class T>
 #if BEAST_DOXYGEN
@@ -50,6 +56,29 @@ struct is_mutable_buffer_sequence :
 {
 };
 
+//------------------------------------------------------------------------------
+//
+// Handler concepts
+//
+//------------------------------------------------------------------------------
+
+/// Determine if `T` meets the requirements of @b CompletionHandler.
+template<class T, class Signature>
+#if BEAST_DOXYGEN
+using is_completion_handler = std::integral_constant<bool, ...>;
+#else
+using is_completion_handler = std::integral_constant<bool,
+    std::is_copy_constructible<typename std::decay<T>::type>::value &&
+        detail::is_invocable<T, Signature>::value>;
+#endif
+
+
+//------------------------------------------------------------------------------
+//
+// Stream concepts
+//
+//------------------------------------------------------------------------------
+
 /// Determine if `T` has the `get_io_service` member.
 template<class T>
 #if BEAST_DOXYGEN
@@ -58,6 +87,25 @@ struct has_get_io_service : std::integral_constant<bool, ...>{};
 using has_get_io_service = typename detail::has_get_io_service<T>::type;
 #endif
 
+/// Returns `T::lowest_layer_type` if it exists, else `T`
+#if BEAST_DOXYGEN
+template<class T>
+struct get_lowest_layer;
+#else
+template<class T, class = void>
+struct get_lowest_layer
+{
+    using type = T;
+};
+
+template<class T>
+struct get_lowest_layer<T, detail::void_t<
+    typename T::lowest_layer_type>>
+{
+    using type = typename T::lowest_layer_type;
+};
+#endif
+
 /// Determine if `T` meets the requirements of @b AsyncReadStream.
 template<class T>
 #if BEAST_DOXYGEN
@@ -108,16 +156,6 @@ using is_sync_stream = std::integral_constant<bool,
     is_sync_read_stream<T>::value && is_sync_write_stream<T>::value>;
 #endif
 
-/// Determine if `T` meets the requirements of @b CompletionHandler.
-template<class T, class Signature>
-#if BEAST_DOXYGEN
-using is_completion_handler = std::integral_constant<bool, ...>;
-#else
-using is_completion_handler = std::integral_constant<bool,
-    std::is_copy_constructible<typename std::decay<T>::type>::value &&
-        detail::is_invocable<T, Signature>::value>;
-#endif
-
 } // beast
 
 #endif

include/beast/websocket/stream.hpp

@@ -107,12 +107,7 @@ public:
 
     /// The type of the lowest layer.
     using lowest_layer_type =
-    #if BEAST_DOXYGEN
-        implementation_defined;
-    #else
-        typename beast::detail::get_lowest_layer<
-            next_layer_type>::type;
-    #endif
+        typename get_lowest_layer<next_layer_type>::type;
 
     /** Move-construct a stream.