[dhooper]

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.

[wahern]

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.

[1] See https://github.com/wahern/autoguess/blob/b44556e4/config.h.g... (that's the 2015 revision, but HEAD has the same code).

[dhooper]

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

[1] https://godbolt.org/z/M7zPYdssP

[rucikir]

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? :)

[1]: https://learn.microsoft.com/en-us/cpp/c-language/typeof-c?vi... [2]: https://developercommunity.visualstudio.com/t/Support-for-ty... [3]: https://gcc.godbolt.org/z/Kn51qrj99

[wahern]

This is gonna haunt me.

Digging through some old code of mine (circa 2009) I found this bit:

  #elif _MSC_VER >= 1310
  #define typeof(type)    __typeof(type)

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.

[1] See https://learn.microsoft.com/en-us/cpp/overview/compiler-vers... for mapping between Visual Studio versions and _MSC_VER.

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.

Source: https://learn.microsoft.com/en-us/archive/msdn-magazine/2002... (See also https://learn.microsoft.com/en-us/archive/msdn-magazine/2005...)