Support binding std::optional<T> implementation to IReference<T> parameters

[jonwis]

Assume I have this IDL:

runtimeclass MyThing {
    Windows.Foundation.IReference<UInt32> GetSize();
}

And my implementation says:

struct MyThing : MyThingT<MyThing> {
    std::optional<uint32_t> m_sizeComputed;
    winrt::Windows::Foundation::IReference<uint32_t> GetSize() {
        if (!m_sizeComputed) {
            return nullptr;
        } else {
            return winrt::box_value(m_sizeComputed.value()).as<winrt::Windows::Foundation<IReference<uint32_t>>>();
    }
}

I'd like this to be easier on the implementation, where instead I can just say:

struct MyThing : MyThingT<MyThing> {
    std::optional<uint32_t> m_sizeComputed;
    const std::optional<uint32_t> GetSize() { return m_sizeComputed; }
}

Is there a way for C++/WinRT's shims to match up IReference<T>-things (properties, returned types, parameters) and auto-convert them to/from std::optional<T>?

[sylveon]

Adding implicit conversion from/to std::optional for IReference should work.

[kennykerr]

Feel free to contribute such a conversion.

[kennykerr]

This feature is available as of 2.0.210930.8.