You can essentially write C in Swift by using UnsafePointer and such. If you avoid using reference types then you won't get any automatic memory management. I don't think it's quite ready to replace C as a kernel or driver language, but it's not that far off.

Is there any open source library that does that? I know in theory many things are possible but it would be great to actually test it/see it in action. I never thought of Swift as a language with zero cost abstractions and deterministic performance. If it works I think it really gives it a leg up.

It's pretty uncommon, so I'm not sure. If I may toot my own horn a bit, you may find the code to my memory dumper interesting:

https://github.com/mikeash/memorydumper2

I also gave a talk on this subject a couple of years ago. It's out of date by now, but the basics are still more or less intact:

https://vimeo.com/107707576

Or peruse the standard library documentation for UnsafePointer, UnsafeRawPointer, UnsafeMutablePointer, and UnsafeRawMutablePointer. These are built-in types that the compiler knows about, and code that uses them should compile down to essentially the same stuff as C pointer code would.

This is especially true in Swift 3, which has many improvements around this type of programming.

> Swift can't do realtime. It has automatic memory management. How do you replace C or C++ with Swift for that?

Of course it can, it is just a matter of OS vendors caring to push it down developers throats.

There are ways to manually manage memory if required to do so, but then you suffer the consequences of dealing with Unsafe*.