Add to_underlying backport (#85)

* Add to_underlying backport

* Update include/kf/stl/backport/utility/detail/to_underlying.h

Co-authored-by: Copilot <[email protected]>

---------

Co-authored-by: Copilot <[email protected]>

Author: SergiusTheBest

include/kf/stl/backport/utility/detail/to_underlying.h

@@ -0,0 +1,15 @@
+#pragma once
+#include <utility>
+
+#if !defined(__cpp_lib_to_underlying) // backport for older compilers
+
+namespace kf
+{
+    template<typename Enum>
+    constexpr auto to_underlying(Enum e) noexcept
+    {
+        return static_cast<std::underlying_type_t<Enum>>(e);
+    }
+}
+
+#endif

include/kf/stl/backport/utility/utility

@@ -0,0 +1,2 @@
+#pragma once
+#include "detail/to_underlying.h"

test/CMakeLists.txt

@@ -48,6 +48,7 @@ wdk_add_driver(kf-test WINVER NTDDI_WIN10 STL
     EncodingDetectorTest.cpp
     IntrusivePtrTest.cpp
     TextDetectorTest.cpp
+    ToUnderlyingTest.cpp
     ScopeExitTest.cpp
     SingletonTest.cpp
     DoubleLinkedListTest.cpp

test/ToUnderlyingTest.cpp

@@ -0,0 +1,13 @@
+#include "pch.h"
+#undef __cpp_lib_to_underlying // pretend that the standard library doesn't provide to_underlying
+#include <kf/stl/backport/utility/detail/to_underlying.h>
+
+enum class Color : uint8_t
+{
+    Red = 1,
+    Green = 2,
+    Blue = 3,
+};
+
+static_assert(kf::to_underlying(Color::Blue) == 3);
+static_assert(std::is_same_v<decltype(kf::to_underlying(Color::Blue)), uint8_t>);