The IPTR simply doesn’t support comparison at all, not even for COM interfaces. The IPTR fails the bonus comparison test, but not through any fault of the Test class. This operator releases any previous wrapped pointer before receiving the new one. The only way to receive a new pointer is to use the & operator. The first parameter to Attach() is always a Test*, so there is no ambiguity in passing just nullptr. A sneaky way to avoid the extra typing is to use the Attach() method to attach a null pointer.However, there are multiple assignment operators,¹ so you have to cast the nullptr to Test* to say, “I am assigning a new pointer to be wrapped.” You can use the assignment operator to assign a nullptr.It is an error to call ptr3.Release() on an empty ptr3. The Release() method releases the wrapped pointer, but there must be a non-null wrapped pointer in the first place.Returning the smart pointer to an empty state can be done in multiple ways. You have to fetch it yourself via GetInterfacePtr() if you want to save it. The IPTR.Detach method does not return the detached pointer. This ensures a linker error if the code ever tries to use that fake interface ID. We give it a dummy ID interface in the form of a reference to a variable that is never defined. The IPTR macro assumes that the IID that corresponds to the alleged interface is named IID_Blah. Litmus test: Assignment from other-type smart pointer Litmus test: Assignment from other-type raw pointer Litmus test: Construction from other-type smart pointer Litmus test: Construction from other-type raw pointer Ptr3.Release() // requires ptr3 be non-empty Assignment from same-type smart pointer #include extern const GUID IID_Test extern const GUID IID_Other using TestPtr = IPTR(Test) using OtherPtr = IPTR(Other)Īuto p = ptr3.GetInterfacePtr() ptr3.Detach() Dummy implementations of AddRef and Release for

We continue our survey of duck-typing requirements of various C++ COM smart pointer libraries by looking at MFC’s IPTR, running it through our standard tests.

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