Avoid assuming MinGW headers don't inherit the same as MSVC

ThreeDeeJay · Apr 18, 2023 · 2133c6d · 2133c6d
1 parent ea903ea
commit 2133c6d
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Showing 3 changed files with 35 additions and 27 deletions.
diff --git a/src/buffer.cpp b/src/buffer.cpp
@@ -182,15 +182,18 @@ Buffer::Buffer(DSound8OAL &parent, bool is8, IDirectSoundBuffer *original) noexc
 
     if(original)
     {
-#ifdef __MINGW32__
         /* MinGW headers do not have IDirectSoundBuffer8 inherit from
          * IDirectSoundBuffer, which MSVC apparently does. Reverse the cast
          * done for Buffer -> IDirectSoundBuffer.
          */
-        Buffer *orig{static_cast<Buffer*>(ds::bit_cast<IDirectSoundBuffer8*>(original))};
-#else
-        Buffer *orig{static_cast<Buffer*>(original)};
-#endif
+        auto upcast = [](auto *orig)
+        {
+            if constexpr(std::is_base_of_v<std::remove_pointer_t<decltype(orig)>,Buffer>)
+                return static_cast<Buffer*>(orig);
+            else
+                return static_cast<Buffer*>(ds::bit_cast<IDirectSoundBuffer8*>(orig));
+        };
+        Buffer *orig{upcast(original)};
         mBuffer = orig->mBuffer;
 
         /* According to MSDN, volume isn't copied. */

diff --git a/src/buffer.h b/src/buffer.h
@@ -5,6 +5,7 @@
 #include <bitset>
 #include <memory>
 #include <mutex>
+#include <type_traits>
 #include <utility>
 
 #include <dsound.h>
@@ -229,17 +230,19 @@ class Buffer final : IDirectSoundBuffer8 {
     DWORD getCurrentMode() const noexcept { return mImmediate.dwMode; }
 
     template<typename T>
-    T as() noexcept { return static_cast<T>(this); }
+    T as() noexcept
+    {
+        /* MinGW headers do not have IDirectSoundBuffer8 inherit from
+         * IDirectSoundBuffer, which MSVC apparently does. IDirectSoundBuffer
+         * is a strict subset of IDirectSoundBuffer8, so the interface is ABI
+         * compatible.
+         */
+        if constexpr(std::is_same_v<T,IDirectSoundBuffer*>
+            && !std::is_base_of_v<IDirectSoundBuffer,Buffer>)
+            return ds::bit_cast<T>(static_cast<IDirectSoundBuffer8*>(this));
+        else
+            return static_cast<T>(this);
+    }
 };
 
-#ifdef __MINGW32__
-/* MinGW headers do not have IDirectSoundBuffer8 inherit from
- * IDirectSoundBuffer, which MSVC apparently does. IDirectSoundBuffer is a
- * subset of IDirectSoundBuffer8, so it should be ABI-compatible.
- */
-template<>
-inline IDirectSoundBuffer *Buffer::as() noexcept
-{ return ds::bit_cast<IDirectSoundBuffer*>(static_cast<IDirectSoundBuffer8*>(this)); }
-#endif
-
 #endif // BUFFER_H
diff --git a/src/dsoundoal.h b/src/dsoundoal.h
@@ -6,6 +6,7 @@
 #include <bitset>
 #include <memory>
 #include <mutex>
+#include <type_traits>
 #include <vector>
 
 #include <dsound.h>
@@ -215,20 +216,21 @@ class DSound8OAL final : IDirectSound8 {
     std::vector<Buffer*> &get3dBuffers() noexcept { return m3dBuffers; }
 
     template<typename T> [[nodiscard]]
-    T as() noexcept { return static_cast<T>(this); }
+    T as() noexcept
+    {
+        /* MinGW headers do not have IDirectSound8 inherit from IDirectSound,
+         * which MSVC apparently does. IDirectSound is a strict subset of
+         * IDirectSound8, so the interface is ABI compatible.
+         */
+        if constexpr(std::is_same_v<T,IDirectSound*>
+            && !std::is_base_of_v<IDirectSound,DSound8OAL>)
+            return ds::bit_cast<T>(static_cast<IDirectSound8*>(this));
+        else
+            return static_cast<T>(this);
+    }
 
     [[nodiscard]]
     static ComPtr<DSound8OAL> Create(bool is8);
 };
 
-#ifdef __MINGW32__
-/* MinGW headers do not have IDirectSound8 inherit from IDirectSound, which
- * MSVC apparently does. IDirectSound is a subset of IDirectSoundBuffer, so it
- * should be ABI-compatible.
- */
-template<>
-inline IDirectSound *DSound8OAL::as() noexcept
-{ return ds::bit_cast<IDirectSound*>(static_cast<IDirectSound8*>(this)); }
-#endif
-
 #endif // DSOUNDOAL_H