From f097f401cbd32df604eee0107715ac35f9231d61 Mon Sep 17 00:00:00 2001
From: Vinnie Falco <vinnie.falco@gmail.com>
Date: Mon, 8 May 2017 16:26:07 -0700
Subject: [PATCH] Consolidate get_lowest_layer in type_traits.hpp

fix #347
---
 CHANGELOG.md                                  |  1 +
 extras/beast/test/fail_stream.hpp             |  2 +-
 include/beast/core/buffered_read_stream.hpp   |  2 +-
 .../beast/core/detail/get_lowest_layer.hpp    | 33 ---------
 include/beast/core/detail/type_traits.hpp     | 33 +++++++++
 include/beast/websocket/stream.hpp            |  2 +-
 test/Jamfile                                  |  1 -
 test/core/CMakeLists.txt                      |  1 -
 test/core/get_lowest_layer.cpp                | 74 -------------------
 test/core/type_traits.cpp                     | 69 ++++++++++++++++-
 10 files changed, 105 insertions(+), 113 deletions(-)
 delete mode 100644 test/core/get_lowest_layer.cpp

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 1757fe2d..21c200a7 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,6 +1,7 @@
 Version 40
 
 * Add to_static_string
+* Consolidate get_lowest_layer in type_traits.hpp
 
 --------------------------------------------------------------------------------
 
diff --git a/extras/beast/test/fail_stream.hpp b/extras/beast/test/fail_stream.hpp
index f6f8127f..fedd0033 100644
--- a/extras/beast/test/fail_stream.hpp
+++ b/extras/beast/test/fail_stream.hpp
@@ -11,7 +11,7 @@
 #include <beast/core/async_result.hpp>
 #include <beast/core/bind_handler.hpp>
 #include <beast/core/error.hpp>
-#include <beast/core/detail/get_lowest_layer.hpp>
+#include <beast/core/detail/type_traits.hpp>
 #include <beast/websocket/teardown.hpp>
 #include <beast/test/fail_counter.hpp>
 #include <boost/optional.hpp>
diff --git a/include/beast/core/buffered_read_stream.hpp b/include/beast/core/buffered_read_stream.hpp
index 31a41ba3..f264a037 100644
--- a/include/beast/core/buffered_read_stream.hpp
+++ b/include/beast/core/buffered_read_stream.hpp
@@ -14,7 +14,7 @@
 #include <beast/core/error.hpp>
 #include <beast/core/stream_concepts.hpp>
 #include <beast/core/multi_buffer.hpp>
-#include <beast/core/detail/get_lowest_layer.hpp>
+#include <beast/core/detail/type_traits.hpp>
 #include <boost/asio/buffer.hpp>
 #include <boost/asio/io_service.hpp>
 #include <cstdint>
diff --git a/include/beast/core/detail/get_lowest_layer.hpp b/include/beast/core/detail/get_lowest_layer.hpp
index 4b199ce6..7dacfb17 100644
--- a/include/beast/core/detail/get_lowest_layer.hpp
+++ b/include/beast/core/detail/get_lowest_layer.hpp
@@ -13,39 +13,6 @@
 namespace beast {
 namespace detail {
 
-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;
-};
-
-// If T has a nested type lowest_layer_type,
-// returns that, else returns T.
-template<class T>
-struct get_lowest_layer
-{
-    using type = typename maybe_get_lowest_layer<T,
-        has_lowest_layer<T>::value>::type;
-};
 
 } // detail
 } // beast
diff --git a/include/beast/core/detail/type_traits.hpp b/include/beast/core/detail/type_traits.hpp
index b667aa31..f5b50c81 100644
--- a/include/beast/core/detail/type_traits.hpp
+++ b/include/beast/core/detail/type_traits.hpp
@@ -127,6 +127,39 @@ 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;
+};
+
 } // detail
 } // beast
 
diff --git a/include/beast/websocket/stream.hpp b/include/beast/websocket/stream.hpp
index da200594..f00f7838 100644
--- a/include/beast/websocket/stream.hpp
+++ b/include/beast/websocket/stream.hpp
@@ -17,7 +17,7 @@
 #include <beast/core/async_result.hpp>
 #include <beast/core/buffered_read_stream.hpp>
 #include <beast/core/string_view.hpp>
-#include <beast/core/detail/get_lowest_layer.hpp>
+#include <beast/core/detail/type_traits.hpp>
 #include <boost/asio.hpp>
 #include <algorithm>
 #include <cstdint>
diff --git a/test/Jamfile b/test/Jamfile
index bfd83dcd..5250cd20 100644
--- a/test/Jamfile
+++ b/test/Jamfile
@@ -40,7 +40,6 @@ unit-test core-tests :
     core/string_view.cpp
     core/base64.cpp
     core/empty_base_optimization.cpp
-    core/get_lowest_layer.cpp
     core/sha1.cpp
     core/type_traits.cpp
     ;
diff --git a/test/core/CMakeLists.txt b/test/core/CMakeLists.txt
index 87c7858a..78a2b769 100644
--- a/test/core/CMakeLists.txt
+++ b/test/core/CMakeLists.txt
@@ -33,7 +33,6 @@ add_executable (core-tests
     string_view.cpp
     base64.cpp
     empty_base_optimization.cpp
-    get_lowest_layer.cpp
     sha1.cpp
     type_traits.cpp
 )
diff --git a/test/core/get_lowest_layer.cpp b/test/core/get_lowest_layer.cpp
deleted file mode 100644
index 315d7e02..00000000
--- a/test/core/get_lowest_layer.cpp
+++ /dev/null
@@ -1,74 +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)
-//
-
-// Test that header file is self-contained.
-#include <beast/core/detail/get_lowest_layer.hpp>
-
-#include <type_traits>
-
-namespace beast {
-namespace detail {
-
-struct F1
-{
-};
-
-struct F2
-{
-};
-
-template<class F>
-struct F3
-{
-    using next_layer_type =
-        typename std::remove_reference<F>::type;
-
-    using lowest_layer_type = typename
-        get_lowest_layer<next_layer_type>::type;
-};
-
-template<class F>
-struct F4
-{
-    using next_layer_type =
-        typename std::remove_reference<F>::type;
-
-    using lowest_layer_type = typename
-        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, "");
-
-static_assert(std::is_same<
-    get_lowest_layer<F2>::type, F2>::value, "");
-
-static_assert(std::is_same<
-    get_lowest_layer<F3<F1>>::type, F1>::value, "");
-
-static_assert(std::is_same<
-    get_lowest_layer<F3<F2>>::type, F2>::value, "");
-
-static_assert(std::is_same<
-    get_lowest_layer<F4<F1>>::type, F1>::value, "");
-
-static_assert(std::is_same<
-    get_lowest_layer<F4<F2>>::type, F2>::value, "");
-
-static_assert(std::is_same<
-    get_lowest_layer<F4<F3<F1>>>::type, F1>::value, "");
-
-static_assert(std::is_same<
-    get_lowest_layer<F4<F3<F2>>>::type, F2>::value, "");
-
-} // detail
-} // beast
diff --git a/test/core/type_traits.cpp b/test/core/type_traits.cpp
index 0f57b040..2c0054ed 100644
--- a/test/core/type_traits.cpp
+++ b/test/core/type_traits.cpp
@@ -10,8 +10,13 @@
 
 namespace beast {
 namespace detail {
+
 namespace {
 
+//
+// is_invocable
+//
+
 struct is_invocable_udt1
 {
     void operator()(int) const;
@@ -51,6 +56,68 @@ static_assert(! is_invocable<
     is_invocable_udt3 const, int(int)>::value, "");
 #endif
 
-}
+//
+// get_lowest_layer
+//
+
+struct F1
+{
+};
+
+struct F2
+{
+};
+
+template<class F>
+struct F3
+{
+    using next_layer_type =
+        typename std::remove_reference<F>::type;
+
+    using lowest_layer_type = typename
+        get_lowest_layer<next_layer_type>::type;
+};
+
+template<class F>
+struct F4
+{
+    using next_layer_type =
+        typename std::remove_reference<F>::type;
+
+    using lowest_layer_type = typename
+        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, "");
+
+static_assert(std::is_same<
+    get_lowest_layer<F2>::type, F2>::value, "");
+
+static_assert(std::is_same<
+    get_lowest_layer<F3<F1>>::type, F1>::value, "");
+
+static_assert(std::is_same<
+    get_lowest_layer<F3<F2>>::type, F2>::value, "");
+
+static_assert(std::is_same<
+    get_lowest_layer<F4<F1>>::type, F1>::value, "");
+
+static_assert(std::is_same<
+    get_lowest_layer<F4<F2>>::type, F2>::value, "");
+
+static_assert(std::is_same<
+    get_lowest_layer<F4<F3<F1>>>::type, F1>::value, "");
+
+static_assert(std::is_same<
+    get_lowest_layer<F4<F3<F2>>>::type, F2>::value, "");
+
+} // (anonymous)
+
 } // detail
 } // beast