Support boxing of GUID types for improved interop (#424)

Author: kennykerr

strings/base_reference_produce.h

@@ -197,6 +197,14 @@ namespace winrt::impl
         static auto make(guid const& value) { return Windows::Foundation::PropertyValue::CreateGuid(value); }
     };
 
+#ifdef __IUnknown_INTERFACE_DEFINED__
+    template <>
+    struct reference_traits<GUID>
+    {
+        static auto make(GUID const& value) { return Windows::Foundation::PropertyValue::CreateGuid(value); }
+    };
+#endif
+
     template <>
     struct reference_traits<Windows::Foundation::DateTime>
     {
@@ -291,6 +299,12 @@ WINRT_EXPORT namespace winrt
                 return static_cast<T>(value.as<Windows::Foundation::IReference<std::underlying_type_t<T>>>().Value());
             }
         }
+#ifdef __IUnknown_INTERFACE_DEFINED__
+        else if constexpr (std::is_same_v<T, GUID>)
+        {
+            return value.as<Windows::Foundation::IReference<guid>>().Value();
+        }
+#endif
         else
         {
             return value.as<Windows::Foundation::IReference<T>>().Value();
@@ -335,6 +349,15 @@ WINRT_EXPORT namespace winrt
                     return static_cast<T>(temp.Value());
                 }
             }
+#ifdef __IUnknown_INTERFACE_DEFINED__
+            else if constexpr (std::is_same_v<T, GUID>)
+            {
+                if (auto temp = value.try_as<Windows::Foundation::IReference<guid>>())
+                {
+                    return temp.Value();
+                }
+            }
+#endif
             else
             {
                 if (auto temp = value.try_as<Windows::Foundation::IReference<T>>())

test/test/box_guid.cpp

@@ -0,0 +1,22 @@
+#include "pch.h"
+
+TEST_CASE("box_guid")
+{
+    winrt::guid const winrt_guid = __uuidof(::IUnknown);
+    GUID const sdk_guid = winrt_guid;
+
+    auto box_a = winrt::box_value(winrt_guid);
+    auto box_b = winrt::box_value(sdk_guid);
+
+    winrt::guid unbox_a = winrt::unbox_value<winrt::guid>(box_a);
+    GUID unbox_b = winrt::unbox_value<GUID>(box_a);
+
+    REQUIRE(unbox_a == winrt_guid);
+    REQUIRE(unbox_b == sdk_guid);
+
+    unbox_a = winrt::unbox_value_or<winrt::guid>(box_a, winrt::guid{});
+    unbox_b = winrt::unbox_value_or<GUID>(box_a, GUID{});
+
+    REQUIRE(unbox_a == winrt_guid);
+    REQUIRE(unbox_b == sdk_guid);
+}

test/test/test.vcxproj

@@ -286,6 +286,7 @@
     <ClCompile Include="async_auto_cancel.cpp" />
     <ClCompile Include="async_cancel_callback.cpp" />
     <ClCompile Include="async_check_cancel.cpp" />
+    <ClCompile Include="box_guid.cpp" />
     <ClCompile Include="error_info.cpp" />
     <ClCompile Include="event_deferral.cpp" />
     <ClCompile Include="async_local.cpp" />