wildthink / SwiftRuntime

How to use Sourcery to recreate the ObjectiveC runtime for your own Swift structs and classes.

SwiftRuntime

How to use Sourcery to recreate the ObjectiveC runtime for your own Swift structs and classes.

Abstract

We'll take a look at how you can leverage Sourcery, the best open-source Swift code-generator to re-create features of the Objective-C runtime in Swift. This is not a Sourcery tutorial. Rather, its intended as a meaningful example of what you can do with a bit of forethought and a small amount of coding with the right tools. Not a contrived example but hopefully something to get you thinking with enough working code to be useful and to build upon.

How-to

Install Sourcery - see Sourcery for more options.

Homebrew

brew install sourcery

If your just tinkering within this download you can just run sourcery from the command line.

$ sourcery --config sourcery.yml

To integrate with your Xcode project, copy the RunSourcery script to somewhere in your $PATH. Add an Xcode Behavior to run the script and you're all set.

Create a Templates and Generated directory in your project and copy the Runtime.stencil into the Templates directory.

For our example, lets create a very simple type to play with. Since using a struct introduces a few wrinkles we use it to illustrate; using classes is more straight forward.

public struct Person {
	public var name: String
}

extension Person: DynamicType {}

$ cd my/project/path; RunSourcery

Add the Generated/*.swift to your project. Make sure you don't copy/move them. Otherwise, Xcode won't see any updates when you regenerate.

Try it out.

var mary = Person(name: "Mary")
let name: String? = mary.lens.get("name", default: nil)

let lens = mary.lens
lens.set("name", to: "Mary Jane")
Swift.print (mary)
// -> Person(name: "Mary")
Swift.print (lens.value()!) 
// -> Person(name: "Mary Jane")