C# Build System (MSBuilds, .csproj): Is there a difference between '#if __IOS__' and '#if IOS' or are they the same?

Question

Essentially what the subject says. I'm getting conflicting information from AI tools on this subject.

Answer 1

And to answer my own question, after experimenting with both I realized that there is in fact a huge difference between the two:

• #if IOS will target only iOS devices (iPhones)

• #if __IOS__ on the other hand will target iOS and MacCatalyst (and possibly other stuff like TvOS, WatchOS, ...)

I find the __IOS__ approach very misleading and dangerous for my taste and here's why. We had a piece of code that was like this:

#if __IOS__
 // do stuff
#end

We then wanted to add special handling for other apple stuff like MacCatalyst. So we tried:

#if __IOS__ // this matches both iOS and MacCatalyst!
 // do stuff
#elif MACCATALYST // wops! this will not be honored because the first #if above already matched MACCATALYST!!
 // do stuff for MacCatalyst
#end

Going forward I will be siding with the explicit approach to avoid such pitfalls

#if IOS // now I know this will only match iOS and nothing else
 // do stuff
#elif MACCATALYST
 // this will now work
#endif

Hope this helps folks out there save a few hours worth of headaches.