Calling Go from Swift

Sat, Oct 3, 2015

Note: Swift bindings are highly experimental and subject to change. This work must currently be classified as preliminary work and we will be improving APIs in the long term.

As a part of the Go Mobile, we have announced tools and packages that make language bindings from Java to Go and Objective-C to Go available. A relatively new and less documented aspect of the bindings is the availability of the Swift to Go calls. This tutorial will explain you how to make your initial Swift to Go function invocation.

Grab the gomobile command and initialize it.

$ go get golang.org/x/mobile/cmd/gomobile
$ gomobile init

In this tutorial, we will use an example Go package from the mobile repo called hello to generate bindings for. The hello package exports a function called Greetings and we will invoke this particular function from a Swift-based iOS app. Go get the example hello package and run gomobile bind to generate a framework bundle.

$ go get golang.org/x/mobile/example/bind/hello/...
$ gomobile bind -target=ios golang.org/x/mobile/example/bind/hello

The command above is going to generate a bundle called Hello.framework on the current working directory which includes a multi-arch C library and a header file.

The next step is to launch Xcode and open your existing Swift-based iOS app project. Drag and drop the Hello.framework to the project. This step will also automatically make the framework library linked to the final app product.

Once the framework bundle is imported, you are good to import the Hello module and invoke GoHelloGreetings which is a proxy function for hello.Greetings.

import UIKit
import Hello
class ViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        println(Hello.GoHelloGreetings("gopher"))
    }
    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
    }
}

Build and run it on your test device or the iOS simulator. Enjoy making your first call to Go from Swift. Please note that this is preliminary work and we would like to make changes to improve the APIs in the long term. More information and tutorials about Go Mobile are available at the wiki.