What is the difference between a Swift package and a module?

Question

Swift has modular code, which can be sorted into modules.

But you can use the Swift Package Manager to fetch and install modules.

Is there any difference between a "Swift package" and a "Swift module"? When should I use one phrase or the other?

Answer 1

As mentioned in Swift.org

Modules: Swift organizes code into modules. Each module specifies a namespace and enforces access controls on which parts of that code can be used outside of the module.

A program may have all of its code in a single module, or it may import other modules as dependencies. Aside from the handful of system-provided modules, such as Darwin on macOS or Glibc on Linux, most dependencies require code to be downloaded and built in order to be used.

When you use a separate module for code that solves a particular problem, that code can be reused in other situations. For example, a module that provides functionality for making network requests can be shared between a photo sharing app and a weather app. Using modules lets you build on top of other developers’ code rather than reimplementing the same functionality yourself.

Packages: A package consists of Swift source files and a manifest file. The manifest file, called Package.swift, defines the package’s name and its contents using the PackageDescription module.

A package has one or more targets. Each target specifies a product and may declare one or more dependencies.

Answer 2

A Swift package is a collection of source code... you can think about it as a self contained project, which has its own versions and repository. The Swift language itself doesn't know about packages currently, it is concept only used by the Swift package manager.

A Swift package can contain one or more Swift modules -- each Swift module is something the language knows about, and the Swift modules defines the scope of things like access control (public, internal, private) for example. A Swift package can also contain other kinds of targets or modules, for example it can contain a body of C source code to build into a library.

Swift packages are in some sense analogous to Xcode projects, and Swift modules are analogous to Xcode targets.

As a concrete example https://github.com/apple/example-package-fisheryates is a Swift package (as signified by the Package.swift at the top-level), identified by its URL, and it contains a single Swift module with two sources: https://github.com/apple/example-package-fisheryates/tree/master/Sources.