Author here. Not quite. The key idea is about using a union to associate type information with a generic data type. Type casting a function is not the only way to use that type information. I discuss that as well as the C23 changes in the footnotes and the "typeof on old compilers" section.
FWIW, as far back as 2015 my feature check library documents Visual Studio as supporting "__typeof".[1] Note the leading but not trailing underscores. Perhaps I was mistaken, but I usually tested that sort of thing. It's also possible __typeof had slightly different semantics.
msvc 19.39 is the first to support it, which I mention in the article. You can confirm it didn't work up through 19.38 in godbolt [1]. I don't use Visual Studio, so I don't know what version of that first started using msvc 19.39
Playing with MSVC's typeof, I've just discovered that its docs [1] have an example that has never worked with any released version of MSVC... MSVC doesn't support `typeof` applied on function types and function pointers! (bug report [2] [3]). Is there anyone from the compiler team around here? :)
So somehow I had the impression Visual Studio .NET 2003 (7.1)[1] added __typeof. I'm still holding out hope someone will come to my rescue and reply that once upon a time MSVC had __typeof, but removed it. But for now it seems past me is gaslighting present me.
EDIT: Ah ha! It seems Microsoft did support __typeof, but perhaps only for "managed" C++ (aka C++ .NET)?
> One thing to watch out for when using the __typeof operator in managed C++ is that __typeof(wchar_t) can return different values depending on the compilation options.
