Add capture support for unconventional result types (#1301)

Author: kennykerr

strings/base_com_ptr.h

@@ -7,16 +7,27 @@ WINRT_EXPORT namespace winrt
 
 namespace winrt::impl
 {
+    struct capture_decay
+    {
+        void** result;
+
+        template <typename T>
+        operator T** ()
+        {
+            return reinterpret_cast<T**>(result);
+        }
+    };
+
     template <typename T, typename F, typename...Args>
     int32_t capture_to(void**result, F function, Args&& ...args)
     {
-        return function(args..., guid_of<T>(), result);
+        return function(args..., guid_of<T>(), capture_decay{ result });
     }
 
     template <typename T, typename O, typename M, typename...Args, std::enable_if_t<std::is_class_v<O> || std::is_union_v<O>, int> = 0>
     int32_t capture_to(void** result, O* object, M method, Args&& ...args)
     {
-        return (object->*method)(args..., guid_of<T>(), result);
+        return (object->*method)(args..., guid_of<T>(), capture_decay{ result });
     }
 
     template <typename T, typename O, typename M, typename...Args>
@@ -343,7 +354,7 @@ namespace winrt::impl
     template <typename T, typename O, typename M, typename...Args>
     int32_t capture_to(void** result, com_ptr<O> const& object, M method, Args&& ...args)
     {
-        return (object.get()->*(method))(args..., guid_of<T>(), result);
+        return (object.get()->*(method))(args..., guid_of<T>(), capture_decay{ result });
     }
 }
 

test/old_tests/UnitTests/capture.cpp

@@ -8,6 +8,7 @@ struct DECLSPEC_UUID("5fb96f8d-409c-42a9-99a7-8a95c1459dbd") ICapture : ::IUnkno
 {
     virtual int32_t __stdcall GetValue() noexcept = 0;
     virtual int32_t __stdcall CreateMemberCapture(int32_t value, GUID const& iid, void** object) noexcept = 0;
+    virtual int32_t __stdcall CreateMemberCapture2(int32_t value, GUID const& iid, ::IUnknown** object) noexcept = 0;
 };
 
 #ifdef __CRT_UUID_DECL
@@ -33,6 +34,12 @@ struct Capture : implements<Capture, ICapture>
         auto capture = make<Capture>(value);
         return capture->QueryInterface(iid, object);
     }
+
+    int32_t __stdcall CreateMemberCapture2(int32_t value, GUID const& iid, ::IUnknown** object) noexcept override
+    {
+        auto capture = make<Capture>(value);
+        return capture->QueryInterface(iid, reinterpret_cast<void**>(object));
+    }
 };
 
 HRESULT __stdcall CreateCapture(int value, GUID const& iid, void** object) noexcept
@@ -41,6 +48,12 @@ HRESULT __stdcall CreateCapture(int value, GUID const& iid, void** object) noexc
     return capture->QueryInterface(iid, object);
 }
 
+HRESULT __stdcall CreateCapture2(int value, GUID const& iid, ::IInspectable** object) noexcept
+{
+    auto capture = make<Capture>(value);
+    return capture->QueryInterface(iid, reinterpret_cast<void**>(object));
+}
+
 TEST_CASE("capture")
 {
     // Capture from global function.
@@ -67,6 +80,19 @@ TEST_CASE("capture")
 
     com_ptr<IDispatch> d;
 
+    // Capture with an unconventional result type.
+    auto e = capture<ICapture>(a, &ICapture::CreateMemberCapture2, 30);
+    REQUIRE(e->GetValue() == 30);
+    e = nullptr;
+    e.capture(a, &ICapture::CreateMemberCapture2, 40);
+    REQUIRE(e->GetValue() == 40);
+
+    com_ptr<ICapture> f = capture<ICapture>(CreateCapture2, 10);
+    REQUIRE(f->GetValue() == 10);
+    f = nullptr;
+    f.capture(CreateCapture2, 20);
+    REQUIRE(a->GetValue() == 20);
+
     REQUIRE_THROWS_AS(capture<IDispatch>(CreateCapture, 0), hresult_no_interface);
     REQUIRE_THROWS_AS(d.capture(CreateCapture, 0), hresult_no_interface);
     REQUIRE_THROWS_AS(capture<IDispatch>(a, &ICapture::CreateMemberCapture, 0), hresult_no_interface);
@@ -104,6 +130,19 @@ TEST_CASE("try_capture")
 
     com_ptr<IDispatch> d;
 
+    // Capture with an unconventional result type.
+    auto e = try_capture<ICapture>(a, &ICapture::CreateMemberCapture2, 30);
+    REQUIRE(e->GetValue() == 30);
+    e = nullptr;
+    REQUIRE(e.try_capture(a, &ICapture::CreateMemberCapture2, 40));
+    REQUIRE(e->GetValue() == 40);
+
+    com_ptr<ICapture> f = try_capture<ICapture>(CreateCapture2, 10);
+    REQUIRE(f->GetValue() == 10);
+    f = nullptr;
+    REQUIRE(f.try_capture(CreateCapture2, 20));
+    REQUIRE(f->GetValue() == 20);
+
     REQUIRE(!try_capture<IDispatch>(CreateCapture, 0));
     REQUIRE(!d.try_capture(CreateCapture, 0));
     REQUIRE(!try_capture<IDispatch>(a, &ICapture::CreateMemberCapture, 0));