Add buffer_traits.hpp, buffers_type

CHANGELOG.md

@@ -5,6 +5,7 @@ Version 198:
 * static_buffer improvements
 * flat_static_buffer_improvements
 * saved_handler maintains a work_guard (websocket)
+* Add buffer_traits.hpp, buffers_type
 
 API Changes:
 

doc/qbk/03_core/3_buffers.qbk

@@ -53,7 +53,7 @@ transferred.
 ][
     This class represents the buffer sequence formed from a prefix of
     an existing buffer sequence. This is the type of buffer returned by
-    [link beast.ref.boost__beast__buffers_prefix.overload3 `buffers_prefix`].
+    [link beast.ref.boost__beast__buffers_prefix `buffers_prefix`].
 ]]
 [[
     [link beast.ref.boost__beast__buffers_range `buffers_range`]

doc/qbk/quickref.xml

@@ -235,6 +235,7 @@
         <entry valign="top">
           <bridgehead renderas="sect3">Type Traits</bridgehead>
           <simplelist type="vert" columns="1">
+            <member><link linkend="beast.ref.boost__beast__buffers_type">buffers_type</link></member>
             <member><link linkend="beast.ref.boost__beast__get_lowest_layer">get_lowest_layer</link></member>
             <member><link linkend="beast.ref.boost__beast__has_get_executor">has_get_executor</link></member>
             <member><link linkend="beast.ref.boost__beast__is_async_read_stream">is_async_read_stream</link></member>

include/boost/beast/core.hpp

@@ -13,6 +13,7 @@
 #include <boost/beast/core/detail/config.hpp>
 
 #include <boost/beast/core/bind_handler.hpp>
+#include <boost/beast/core/buffer_traits.hpp>
 #include <boost/beast/core/buffered_read_stream.hpp>
 #include <boost/beast/core/buffers_adapter.hpp>
 #include <boost/beast/core/buffers_cat.hpp>

include/boost/beast/core/buffer_traits.hpp

@@ -0,0 +1,73 @@
+//
+// Copyright (c) 2018 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)
+//
+// Official repository: https://github.com/boostorg/beast
+//
+
+#ifndef BOOST_BEAST_BUFFER_TRAITS_HPP
+#define BOOST_BEAST_BUFFER_TRAITS_HPP
+
+#include <boost/beast/core/detail/config.hpp>
+#include <boost/asio/buffer.hpp>
+#include <type_traits>
+
+namespace boost {
+namespace beast {
+
+/** Type alias used to obtain the underlying buffer type of a buffer sequence.
+
+    This metafunction is used to determine the underlying buffer type for
+    a given buffer sequence. The equivalent type of the alias will vary
+    depending on the template type argument:
+
+    @li If the template argument is a <em>MutableBufferSequence</em>,
+        the resulting type alias will be `net::mutable_buffer`, else
+
+    @li If the template argument is a <em>ConstBufferSequence</em>,
+        the resulting type alias will be `net::const_buffer`, otherwise
+
+    @li The resulting type alias will be `void`.
+
+    @par Example
+    The following code returns the first buffer in a buffer sequence,
+    or generates a compilation error if the argument is not a buffer
+    sequence:
+    @code
+    template <class BufferSequence>
+    buffers_type <BufferSequence>
+    buffers_front (BufferSequence const& buffers)
+    {
+        static_assert(
+            net::is_const_buffer_sequence<BufferSequence>::value,
+            "BufferSequence requirements not met");
+        auto const first = net::buffer_sequence_begin (buffers);
+        if (first == net::buffer_sequence_end (buffers))
+            return {};
+        return *first;
+    }
+    @endcode
+
+    @param T The buffer sequence type to use.
+*/
+template<class T>
+#if BOOST_BEAST_DOXYGEN
+struct buffers_type : __see_below__ {};
+//using buffers_type = __see_below__;
+#else
+using buffers_type = typename
+    std::conditional<
+        net::is_mutable_buffer_sequence<T>::value,
+        net::mutable_buffer,
+        typename std::conditional<
+            net::is_const_buffer_sequence<T>::value,
+            net::const_buffer,
+            void>::type>::type;
+#endif
+
+} // beast
+} // boost
+
+#endif

test/beast/core/CMakeLists.txt

@@ -20,6 +20,7 @@ add_executable (tests-beast-core
     file_test.hpp
     bind_handler.cpp
     buffer.cpp
+    buffer_traits.cpp
     buffered_read_stream.cpp
     buffers_adapter.cpp
     buffers_cat.cpp

test/beast/core/Jamfile

@@ -10,6 +10,7 @@
 local SOURCES =
     bind_handler.cpp
     buffer.cpp
+    buffer_traits.cpp
     buffered_read_stream.cpp
     buffers_adapter.cpp
     buffers_cat.cpp

test/beast/core/buffer_traits.cpp

@@ -0,0 +1,39 @@
+//
+// Copyright (c) 2018 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)
+//
+// Official repository: https://github.com/boostorg/beast
+//
+
+// Test that header file is self-contained.
+#include <boost/beast/core/buffer_traits.hpp>
+
+#include <array>
+
+namespace boost {
+namespace beast {
+
+BOOST_STATIC_ASSERT(
+    std::is_same<net::const_buffer,
+    buffers_type<net::const_buffer>>::value);
+
+BOOST_STATIC_ASSERT(
+    std::is_same<net::mutable_buffer,
+    buffers_type<net::mutable_buffer>>::value);
+
+BOOST_STATIC_ASSERT(
+    std::is_same<net::const_buffer,
+    buffers_type<std::array<net::const_buffer, 3>>>::value);
+
+BOOST_STATIC_ASSERT(
+    std::is_same<net::mutable_buffer,
+    buffers_type<std::array<net::mutable_buffer, 3>>>::value);
+
+BOOST_STATIC_ASSERT(
+    std::is_same<void,
+    buffers_type<std::array<int, 3>>>::value);
+
+} // beast
+} // boost