fixing 'no matching overloaded function found'

Question

What compiler setting(s) do I need to set in order to avoid:

Error C2672 'unbox_value_type': no matching overloaded function found C:\Program Files (x86)\Windows Kits\10\Include\10.0.22000.0\cppwinrt\winrt\Windows.Foundation.h 2901

The Windows.Foundation.h file is read only, and I'd like to keep it that way.

I'm trying to create a Windows application that uses WebView2. I installed VS2022 (free version), downloaded the WebView2 sample (the sample solution builds OK). I created a new project, and I'm trying to add fragments to it from the sample, but the compiler errors out on the file mentioned above, on line 2901.

Answer 1

You need to #include <unknwn.h> before any cppwinrt header to enable classic COM support.

Useful reading (both articles written by Raymond Chen):

• Why does C++/WinRT say that first_interface is not a member of winrt::impl::interface_list<>?

  I noted that by default C++/WinRT requires interfaces to derive from winrt::Windows::Foundation::IUnknown. You can activate nondefault behavior by including the unknwn.h header file before including any C++/WinRT header files, in which case C++/WinRT will also recognize types which derives from classic COM IUnknown as interfaces.

• The various ways of moving between C++/WinRT and classic COM