Tidy up is_dynamic_buffer traits test

CHANGELOG.md

@@ -8,6 +8,7 @@ Version 44
 * Fix async return values in docs
 * Fix README websocket example
 * Add buffers_adapter regression test
+* Tidy up is_dynamic_buffer traits test
 
 --------------------------------------------------------------------------------
 

include/beast/core/detail/type_traits.hpp

@@ -198,81 +198,6 @@ public:
         type3::value && type4::value>;
 };
 
-template<class T>
-class is_dynamic_buffer
-{
-    // size()
-    template<class U, class R = std::is_convertible<decltype(
-        std::declval<U const>().size()), std::size_t>>
-    static R check1(int);
-    template<class>
-    static std::false_type check1(...);
-    using type1 = decltype(check1<T>(0));
-
-    // max_size()
-    template<class U, class R = std::is_convertible<decltype(
-        std::declval<U const>().max_size()), std::size_t>>
-    static R check2(int);
-    template<class>
-    static std::false_type check2(...);
-    using type2 = decltype(check2<T>(0));
-
-    // capacity()
-    template<class U, class R = std::is_convertible<decltype(
-        std::declval<U const>().capacity()), std::size_t>>
-    static R check3(int);
-    template<class>
-    static std::false_type check3(...);
-    using type3 = decltype(check3<T>(0));
-
-    // data()
-    template<class U, class R = std::integral_constant<
-        bool, is_buffer_sequence<decltype(
-            std::declval<U const>().data()),
-                boost::asio::const_buffer>::type::value>>
-    static R check4(int);
-    template<class>
-    static std::false_type check4(...);
-    using type4 = decltype(check4<T>(0));
-
-    // prepare()
-    template<class U, class R = std::integral_constant<
-        bool, is_buffer_sequence<decltype(
-            std::declval<U>().prepare(1)),
-                boost::asio::mutable_buffer>::type::value>>
-    static R check5(int);
-    template<class>
-    static std::false_type check5(...);
-    using type5 = decltype(check5<T>(0));
-
-    // commit()
-    template<class U, class R = decltype(
-        std::declval<U>().commit(1), std::true_type{})>
-    static R check6(int);
-    template<class>
-    static std::false_type check6(...);
-    using type6 = decltype(check6<T>(0));
-
-    // consume
-    template<class U, class R = decltype(
-        std::declval<U>().consume(1), std::true_type{})>
-    static R check7(int);
-    template<class>
-    static std::false_type check7(...);
-    using type7 = decltype(check7<T>(0));
-
-public:
-    using type = std::integral_constant<bool,
-        type1::value
-        && type2::value
-        //&& type3::value // Networking TS
-        && type4::value
-        && type5::value
-        && type6::value
-        && type7::value
-    >;
-};
-
 //------------------------------------------------------------------------------
 
 template<class B1, class... Bn>

include/beast/core/type_traits.hpp

@@ -33,17 +33,6 @@ struct is_const_buffer_sequence :
 {
 };
 
-/// Determine if `T` meets the requirements of @b DynamicBuffer.
-template<class T>
-#if BEAST_DOXYGEN
-struct is_dynamic_buffer : std::integral_constant<bool, ...>
-#else
-struct is_dynamic_buffer :
-    detail::is_dynamic_buffer<T>::type
-#endif
-{
-};
-
 /// Determine if `T` meets the requirements of @b MutableBufferSequence.
 template<class T>
 #if BEAST_DOXYGEN
@@ -56,6 +45,45 @@ struct is_mutable_buffer_sequence :
 {
 };
 
+/// Determine if `T` meets the requirements of @b DynamicBuffer.
+#if BEAST_DOXYGEN
+template<class T>
+struct is_dynamic_buffer : std::integral_constant<bool, ...> {};
+#else
+template<class T, class = void>
+struct is_dynamic_buffer : std::false_type {};
+
+template<class T>
+struct is_dynamic_buffer<T, beast::detail::void_t<
+        decltype(
+    // expressions
+    std::declval<std::size_t&>() =
+        std::declval<T const&>().size(),
+    std::declval<std::size_t&>() =
+        std::declval<T const&>().max_size(),
+#if 0
+    // This check is skipped because boost::asio
+    // types are not up to date with net-ts.
+    std::declval<std::size_t&>() =
+        std::declval<T const&>().capacity(),
+#endif
+    std::declval<T&>().commit(std::declval<std::size_t>()),
+    std::declval<T&>().consume(std::declval<std::size_t>()),
+        (void)0)>> : std::integral_constant<bool,
+    is_const_buffer_sequence<
+        typename T::const_buffers_type>::value &&
+    is_mutable_buffer_sequence<
+        typename T::mutable_buffers_type>::value &&
+    std::is_same<typename T::const_buffers_type,
+        decltype(std::declval<T const&>().data())>::value &&
+    std::is_same<typename T::mutable_buffers_type,
+        decltype(std::declval<T&>().prepare(
+            std::declval<std::size_t>()))>::value
+        >
+{
+};
+#endif
+
 //------------------------------------------------------------------------------
 //
 // Handler concepts

test/core/type_traits.cpp

@@ -9,6 +9,7 @@
 #include <beast/core/type_traits.hpp>
 
 #include <boost/asio/ip/tcp.hpp>
+#include <boost/asio/streambuf.hpp>
 
 namespace beast {
 
@@ -100,6 +101,8 @@ BOOST_STATIC_ASSERT(! is_const_buffer_sequence<T>::value);
 BOOST_STATIC_ASSERT(is_mutable_buffer_sequence<detail::MutableBufferSequence>::value);
 BOOST_STATIC_ASSERT(! is_mutable_buffer_sequence<T>::value);
 
+BOOST_STATIC_ASSERT(is_dynamic_buffer<boost::asio::streambuf>::value);
+
 } // (anonymous)
 
 //