Creating New Packages with SwiftPM

Back in December I opened an enhancement request in the Swift JIRA site, issue SR-353, to add an npm init-style invocation to swift build for creating all of the boilerplate files needed for a complete Swift package. It wasn’t too long after the request was added that Bastian Rinsche and Tobias Landsberg implemented the feature and had a pull request accepted. Bastian has written up a great post on his experience with opensource Swift and contributing to the community with the implementation of swift build --init.

Let’s look at how it works. First, create a new directory with mkdir for your package or application. We’ll use helloworld as an example: mkdir helloworld. Now, cd into your helloworld directory and run swift build --init.

# cd helloworld
# swift build --init
Creating Package.swift
Creating .gitignore
Creating Sources/
Creating Sources/main.swift
Creating Tests/

Let’s take a look at what swift build --init generates:

• Package.swift – the “manifest” for this package; swift build --init names your package the same as the directory you invoked it in
• Sources – SwiftPM convention is that source files are included in a directory called Sources
• main.swift – Swift applications will have one (and only one) main.swift file as the execution entry point
• Tests – a directory to hold testcases for the application; more on this in a moment
• .gitignore – a handy Git gitignore starter file that ignores build artifacts such as .build and Packages (things you don’t want to check in to a repository)

In our helloworld example Package.swift looks like this:

Running swift build at this point will create .build/debug/helloworld which when executed you will see Hello, world!.

If you are building a Swift-based library then remove main.swift and replace it with your library code. Without a main.swift SwiftPM will create a static library archive.

Tests

The Tests directory added by swift build --init is a nod to the future implementation of SR-592, which tracks SE-0019, Swift Package Manager support for automated testing.

Getting the Ubuntu Package

To get started with swift build --init you can grab the latest Ubuntu package for Swift 2.2 (as of this writing, version 2.2-0ubuntu15). See this post for instructions. For more details about using SwiftPM in general, see our introduction here. Happy Swifting!