[swift-users] C/FFI interop

Jason Dusek jason.dusek at gmail.com
Wed Dec 23 18:20:50 CST 2015

I think the OP was asking not about importing C symbols into Swift but
rather exporting Swift to C.

On Wed, 23 Dec 2015 at 15:18 Brent Royal-Gordon via swift-users <
swift-users at swift.org> wrote:

> > What are the current facilities planned or in development for FFI? Just
> as Swift functions can be exposed through @objc, how would I add a similar
> capability for pure C? Is this what, in fact, module maps might be for?
> >
> > I ask since writing high performance native code for dynamic languages
> is currently done in C, and that’s a pretty bad idea. It would be great for
> Swift if people started writing native bindings in it as opposed to C, but
> it probably needs at the least a way to re-export global public functions
> for C/C++.
> >
> > Please let me know if I should take this to swift-dev or swift-evolution!
> Swift does not require a foreign function interface—it can directly call C
> functions. Sometimes Swift generates a trampoline to do this, but often not
> even that. The module map basically just tells Swift which headers and
> binaries make up a particular module. There's generally no need to write
> any bridging code—it just works.
> There are a few C constructs that Swift doesn't support very well, like
> unions and fixed-size arrays in structs. In those cases, you may need to
> write some C functions which perform the operations that can't be easily
> expressed in Swift, but these functions would just be plain old C with no
> special bridging involved. Similarly, you may choose to write wrappers
> around some of your library's C constructs to make them more convenient to
> use—for instance, if your library has a struct called `foo` and an
> operation on that struct called `frobnicate_foo()`, you might extend `foo`
> to add a `frobnicate()` method to it. But this is purely optional, and you
> would write it in plain old Swift.
> Though Apple's platforms are most commonly associated with Objective-C,
> there's a lot of C over there too. Swift works very well with it—this stuff
> is fast, as transparent as it can be, and frequently exercised.
> In short: Just try it. It's pretty easy.
> --
> Brent Royal-Gordon
> Architechies
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> swift-users at swift.org
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