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Developing Packages

Simply put: a package is a git repository with semantically versioned tags, that contains Swift sources and a Package.swift manifest file at its root.

Turning a Library Module into an External Package

If you are building an app with several modules, at some point you may decide to make that module into an external package. Doing this makes that code available as a dependable library that others may use.

Doing so with the package manager is relatively simple:

  1. Create a new repository on GitHub
  2. In a terminal, step into the module directory
  3. git init
  4. git remote add origin [github-URL]
  5. git add .
  6. git commit --message="…"
  7. git tag 1.0.0
  8. git push origin master --tags

Now delete the subdirectory, and amend your Package.swift so that its package declaration includes:

let package = Package(
    dependencies: [
        .Package(url: "…", versions: Version(1,0,0)..<Version(2,0,0)),
    ]
)

Now type swift build

Working on Apps and Packages Side-by-Side

If you are developing an app that consumes a package and you need to work on that package simultaneously then you have several options:

  1. Edit the sources the package manager clones

    The sources are cloned visibly into ./Packages to facilitate this.

  2. Alter your Package.swift so it refers to a local clone of the package

    This can be tedious however as you will need to force an update every time you make a change, including updating the version tag.

Both options are currently non-ideal since it is easy to commit code that will break for other members of your team, for example, if you change the sources for Foo and then commit a change to your app that uses those new changes but you have not committed those changes to Foo then you have caused dependency hell for your co-workers.

It is our intention to provide tooling to prevent such situations, but for now please be aware of the caveats.

Packaging legacy code

You may be working with code that builds both as a package and not. For example, you may be packaging a project that also builds with Xcode.

In these cases, you can use the build configuration SWIFT_PACKAGE to conditionally compile code for Swift packages.

#if SWIFT_PACKAGE
import Foundation
#endif