Showcases how to create a stack allocated Windows Runtime object

StackWinRT.cpp

#include <iostream>
#include <Windows.h>
#include <winstring.h>
#include <Windows.Foundation.h>

#pragma comment(lib, "OneCoreUAP.lib")

struct StackStringable final : ABI::Windows::Foundation::IStringable
{
public:
    ULONG __stdcall AddRef()
    {
        return InterlockedIncrement(&m_ReferenceCount);
    }

    ULONG __stdcall Release()
    {
        return InterlockedDecrement(&m_ReferenceCount);
    }

    HRESULT __stdcall QueryInterface(REFIID riid, void** ppvObject)
    {
        if (riid == __uuidof(IUnknown))
        {
            *ppvObject = static_cast<IUnknown*>(this);
            AddRef();
            return S_OK;
        }
        else if (riid == __uuidof(IInspectable))
        {
            *ppvObject = static_cast<IInspectable*>(this);
            AddRef();
            return S_OK;
        }
        else if (riid == __uuidof(ABI::Windows::Foundation::IStringable))
        {
            *ppvObject = static_cast<ABI::Windows::Foundation::IStringable*>(this);
            AddRef();
            return S_OK;
        }
        else return E_NOINTERFACE;
    }

    HRESULT __stdcall GetIids(ULONG* iidCount, IID** iids)
    {
        auto array = static_cast<IID*>(CoTaskMemAlloc(sizeof(IID)));
        if (array == nullptr) return E_OUTOFMEMORY;
        else
        {
            array[0] = __uuidof(ABI::Windows::Foundation::IStringable);
            *iidCount = 1;
            *iids = array;
            return S_OK;
        }
    }

    HRESULT __stdcall GetRuntimeClassName(HSTRING* className)
    {
        return WindowsCreateString(InterfaceName_Windows_Foundation_IStringable, _countof(InterfaceName_Windows_Foundation_IStringable), className);
    }

    HRESULT __stdcall GetTrustLevel(TrustLevel* trustLevel)
    {
        *trustLevel = TrustLevel::FullTrust;
        return S_OK;
    }

    HRESULT __stdcall ToString(HSTRING* value)
    {
       return WindowsCreateString(L"This message is from StackStringable.", 37, value);
    }
private:
    ULONG m_ReferenceCount = 1;
};

struct HeapStringable final : ABI::Windows::Foundation::IStringable
{
public:
    ULONG __stdcall AddRef()
    {
        return InterlockedIncrement(&m_ReferenceCount);
    }

    ULONG __stdcall Release()
    {
        auto count = InterlockedDecrement(&m_ReferenceCount);
        if (count == 0) delete this;
        return count;
    }

    HRESULT __stdcall QueryInterface(REFIID riid, void** ppvObject)
    {
        if (riid == __uuidof(IUnknown))
        {
            *ppvObject = static_cast<IUnknown*>(this);
            AddRef();
            return S_OK;
        }
        else if (riid == __uuidof(IInspectable))
        {
            *ppvObject = static_cast<IInspectable*>(this);
            AddRef();
            return S_OK;
        }
        else if (riid == __uuidof(ABI::Windows::Foundation::IStringable))
        {
            *ppvObject = static_cast<ABI::Windows::Foundation::IStringable*>(this);
            AddRef();
            return S_OK;
        }
        else return E_NOINTERFACE;
    }

    HRESULT __stdcall GetIids(ULONG* iidCount, IID** iids)
    {
        auto array = static_cast<IID*>(CoTaskMemAlloc(sizeof(IID)));
        if (array == nullptr) return E_OUTOFMEMORY;
        else
        {
            array[0] = __uuidof(ABI::Windows::Foundation::IStringable);
            *iidCount = 1;
            *iids = array;
            return S_OK;
        }
    }

    HRESULT __stdcall GetRuntimeClassName(HSTRING* className)
    {
        return WindowsCreateString(InterfaceName_Windows_Foundation_IStringable, _countof(InterfaceName_Windows_Foundation_IStringable), className);
    }

    HRESULT __stdcall GetTrustLevel(TrustLevel* trustLevel)
    {
        *trustLevel = TrustLevel::FullTrust;
        return S_OK;
    }

    HRESULT __stdcall ToString(HSTRING* value)
    {
        return WindowsCreateString(L"This message is from HeapStringable.", 36, value);
    }
private:
    ULONG m_ReferenceCount = 1;
};

void PrintStringable(ABI::Windows::Foundation::IStringable* stringable)
{
    HSTRING text;
    stringable->ToString(&text);
    std::wcout << WindowsGetStringRawBuffer(text, nullptr) << L"\n";
    WindowsDeleteString(text);
}

int main()
{
    StackStringable stackStringable;
    PrintStringable(&stackStringable);
    stackStringable->Release();
    auto heapStringable = new HeapStringable();
    PrintStringable(heapStringable);
    heapStringable->Release();
    return 0;
}