Tidy up and make get_lowest_layer public

fix #379

CHANGELOG.md

@@ -3,6 +3,7 @@ Version 44
 * Use BOOST_THROW_EXCEPTION
 * Tidy up read_size_helper and dynamic buffers
 * Require Boost 1.58.0 or later
+* Tidy up and make get_lowest_layer public
 
 --------------------------------------------------------------------------------
 

doc/core.qbk

@@ -38,6 +38,11 @@ diagnostics.
 
 [table Type Traits
 [[Name][Description]]
+[[
+    [link beast.ref.get_lowest_layer `get_lowest_layer`]
+][
+    Returns `T::lowest_layer_type` if it exists, else returns `T`.
+]]
 [[
     [link beast.ref.has_get_io_service `has_get_io_service`]
 ][

doc/overview.qbk

@@ -139,6 +139,7 @@ Asio library and the ideas upon which Beast is built.
 Beast would not be possible without the considerable time and patience
 contributed by David Schwartz, Edward Hennis, Howard Hinnant, Miguel Portilla,
 Nikolaos Bougalis, Scott Determan, Scott Schurr, and Ripple Labs for
-supporting its early development.
+supporting its early development. Also thanks to Agustín Bergé, Glen Fernandes
+and Peter Dimov for putting up with my endless C++ questions on Slack.
 
 [endsect]

doc/quickref.xml

@@ -194,6 +194,7 @@
         <entry valign="top">
           <bridgehead renderas="sect3">Type Traits</bridgehead>
           <simplelist type="vert" columns="1">
+            <member><link linkend="beast.ref.get_lowest_layer">get_lowest_layer</link></member>
             <member><link linkend="beast.ref.has_get_io_service">has_get_io_service</link></member>
             <member><link linkend="beast.ref.is_async_read_stream">is_async_read_stream</link></member>
             <member><link linkend="beast.ref.is_async_write_stream">is_async_write_stream</link></member>

extras/beast/test/fail_stream.hpp

@@ -36,8 +36,7 @@ public:
         typename std::remove_reference<NextLayer>::type;
 
     using lowest_layer_type =
-        typename beast::detail::get_lowest_layer<
+        typename get_lowest_layer<next_layer_type>::type;
-            next_layer_type>::type;
 
     fail_stream(fail_stream&&) = delete;
     fail_stream(fail_stream const&) = delete;

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
+        typename get_lowest_layer<next_layer_type>::type;
-        implementation_defined;
-#else
-        typename detail::get_lowest_layer<
-            next_layer_type>::type;
-#endif
 
     /** 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
+        typename get_lowest_layer<next_layer_type>::type;
-        implementation_defined;
-    #else
-        typename beast::detail::get_lowest_layer<
-            next_layer_type>::type;
-    #endif
 
     /** Move-construct a stream.
 

test/core/type_traits.cpp

@@ -86,11 +86,6 @@ struct F4
         get_lowest_layer<next_layer_type>::type;
 };
 
-static_assert(! has_lowest_layer<F1>::value, "");
-static_assert(! has_lowest_layer<F2>::value, "");
-static_assert(has_lowest_layer<F3<F1>>::value, "");
-static_assert(has_lowest_layer<F4<F3<F2>>>::value, "");
-
 static_assert(std::is_same<
     get_lowest_layer<F1>::type, F1>::value, "");