[swift-users] C/FFI interop

Thomas Catterall me at swizzlr.co
Wed Dec 23 19:53:54 CST 2015

Indeed I was - I'm quite sorry for the confusion, I didn't make my intent clear as I should have, such as through example. What I'm referring to is, for instance, offering a way for a Ruby library to interface with a module written in Swift to communicate with Redis (as an example, not something I'm thinking too seriously about).

Sent from my iPhone

> On 23 Dec 2015, at 19:20, Jason Dusek <jason.dusek at gmail.com> wrote:
> 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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