Add SLANG_IID_PPV_ARGS (#2784)

* Add SLANG_IID_PPV_ARGS

To mirror IID_PPV_ARGS from the COM Coding Practices: https://learn.microsoft.com/en-us/windows/win32/LearnWin32/com-coding-practices#the-iid_ppv_args-macro

* Make getTypeGuid constexpr

---------

Co-authored-by: Yong He <yonghe@outlook.com>

1 files changed, 18 insertions, 6 deletions

diff --git a/slang.h b/slang.h
index d5630660b..5dd2cb550 100644
--- a/slang.h
+++ b/slang.h
@@ -932,21 +932,33 @@ extern "C"
 // It is not necessary to use the multiple parameters (we can wrap in parens), but this is simple.
 #define SLANG_COM_INTERFACE(a, b, c, d0, d1, d2, d3, d4, d5, d6, d7) \
     public: \
-    SLANG_FORCE_INLINE static const SlangUUID& getTypeGuid() \
+    SLANG_FORCE_INLINE constexpr static SlangUUID getTypeGuid() \
     { \
-        static const SlangUUID guid = { a, b, c, d0, d1, d2, d3, d4, d5, d6, d7 }; \
-        return guid; \
+        return { a, b, c, d0, d1, d2, d3, d4, d5, d6, d7 }; \
     }
 
 // Sometimes it's useful to associate a guid with a class to identify it. This macro can used for this,
 // and the guid extracted via the getTypeGuid() function defined in the type
 #define SLANG_CLASS_GUID(a, b, c, d0, d1, d2, d3, d4, d5, d6, d7) \
-    SLANG_FORCE_INLINE static const SlangUUID& getTypeGuid() \
+    SLANG_FORCE_INLINE constexpr static SlangUUID getTypeGuid() \
     { \
-        static const SlangUUID guid = { a, b, c, d0, d1, d2, d3, d4, d5, d6, d7 }; \
-        return guid; \
+        return { a, b, c, d0, d1, d2, d3, d4, d5, d6, d7 }; \
     }
 
+// Helper to fill in pairs of GUIDs and return pointers. This ensures that the
+// type of the GUID passed matches the pointer type, and that it is derived
+// from ISlangUnknown,
+// TODO(c++20): would is_derived_from be more appropriate here for private inheritance of ISlangUnknown?
+//
+// with     : void createFoo(SlangUUID, void**);
+//            Slang::ComPtr<Bar> myBar;
+// call with: createFoo(SLANG_IID_PPV_ARGS(myBar.writeRef()))
+// to call  : createFoo(Bar::getTypeGuid(), (void**)(myBar.writeRef()))
+#define SLANG_IID_PPV_ARGS(ppType) \
+    std::decay_t<decltype(**(ppType))>::getTypeGuid(), \
+    ((void)[]{static_assert(std::is_base_of_v<ISlangUnknown, std::decay_t<decltype(**(ppType))>>);}, reinterpret_cast<void**>(ppType))
+
+
     /** Base interface for components exchanged through the API.
 
     This interface definition is compatible with the COM `IUnknown`,