C++/WinRT support for implementing COM interfaces that derive from ::IInspectable

[kennykerr]

Ideally this would not be required, but regrettably there exists some COM interop interfaces that just happen to derive from ::IInspectable. This update makes it easier to implement such interfaces in C++/WinRT.

This now "just works" provided you include <inspectable.h> before including any C++/WinRT headers. This is distinct from general COM interop support that merely requires that you include <unknwn.h> because changing that now would break the world.

struct __declspec(uuid("ed0dd761-c31e-4803-8cf9-22a2cb20ec47")) IBadInterop : ::IInspectable
{
    virtual int32_t __stdcall JustSayNo() noexcept = 0;
};

struct Sample : implements<Sample, Windows::Foundation::IActivationFactory, IBadInterop>
{
    Windows::Foundation::IInspectable ActivateInstance()
    {
        throw hresult_not_implemented();
    }

    hstring GetRuntimeClassName()
    {
        return L"Sample";
    }

    Windows::Foundation::TrustLevel GetTrustLevel()
    {
        return Windows::Foundation::TrustLevel::PartialTrust;
    }

    int32_t __stdcall JustSayNo() noexcept final
    {
        return 123;
    }
};

[oldnewthing]

In practice, this IBadInterop definition would come from some ABI header file, right?

[kennykerr]

Right.