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Code structure and organization is a matter of pride for developers. Clear and consistent code signifies clear and consistent thought. Even though the compiler lacks a discerning palate when it comes to naming, whitespace, or documentation, it makes all the difference for human collaborators.
This week, we’ll be documenting the here and now of documentation in Swift.
Since the early ’00s, Headerdoc has been Apple’s preferred documentation standard. Starting off as little more than a Perl script that parsed trumped-up Javadoc comments, Headerdoc would eventually be the engine behind Apple’s developer documentation online and in Xcode.
But like so much of the Apple developer ecosystem, Swift changed everything. In the spirit of “Out with the old, in with the new”, Xcode 7 traded Headerdoc for fan favorite Markdown — specifically, Swift-flavored Markdown.
Even if you’ve never written a line of Markdown before, you can get up to speed in just a few minutes. Here’s pretty much everything you need to know:
Documentation comments look like normal comments, but with a little something extra. Single-line documentation comments have three slashes (
///). Multi-line documentation comments have an extra star in their opening delimiter (
/** ... */).
Standard Markdown rules apply inside documentation comments:
1.) or a right parenthesis (
#signs or underlined with
The leading paragraph of a documentation comment becomes the documentation Summary. Any additional content is grouped together into the Discussion section.
If a documentation comment starts with anything other than a paragraph, all of its content is put into the Discussion.
Xcode recognizes a few special fields and makes them separate from a symbol’s description. The parameters, return value, and throws sections are broken out in the Quick Help popover and inspector when styled as a bulleted item followed by a colon (
Parameter <param name>:and the description of the parameter.
Returns:and information about the return value.
Throws:and a description of the errors that can be thrown. Since Swift doesn’t type-check thrown errors beyond
Errorconformance, it’s especially important to document errors properly.
Are you documenting a function whose method signature has more arguments than a Hacker News thread about tabs vs. spaces? Break out your parameters into a bulleted list underneath a
In addition to
Returns, Swift-flavored Markdown defines a handful of other fields, which can be loosely organized in the following way:
Each of these fields is rendered in Quick Help as a bold header followed by a block of text:
The text of the subfield is displayed starting on the next line.
Demonstrate the proper usage or implementation details of a function by embedding code blocks. Inset code blocks by at least four spaces:
Fenced code blocks are also recognized, delimited by either three backticks (
`) or tildes (
How does this look when applied to an entire class? Quite nice, actually!
Option-click on the initializer declaration, and the description renders beautifully with a bulleted list:
Open Quick Documentation for the method
travel, and the parameter is parsed out into a separate field, as expected:
In Objective-C, the preprocessor directive
#pragma mark is used to divide functionality into meaningful, easy-to-navigate sections. In Swift, the same can be accomplished with the comment
The following comments are surfaced in the Xcode source navigator:
Other conventional comment tags, such as
XXX aren’t recognized by Xcode.
#pragma, marks followed by a single dash (
-) are preceded with a horizontal divider
To show these new tags in action, here’s how the
Bicycle class could be extended to adopt the
CustomStringConvertible protocol, and implement the
Bringing everything together in code:
At the time of writing, there’s no official tool for transforming documentation comments into something more tangible than Quick Help panels in Xcode,
Fortunately, where necessity arises, open source (often) delivers.
Jazzy is a terrific open-source command-line utility that transforms your project’s documentation comments into a set of Apple-like HTML documentation (but that nice vintage style, before that whole redesign). Jazzy uses Xcode’s SourceKitService to read your beautifully written type and method descriptions.
Install Jazzy as a gem, then run from the root of your project folder to generate documentation.
Take a peek at a Jazzy-generated documentation for the
Although the tooling and documentation around Swift is still developing, one would be wise to adopt good habits early, by using the new Markdown capabilities for documentation, as well as
MARK: comments in Swift code going forward.
Go ahead and add it to your
Whether you're building for Android handsets, Wear OS by Google, Android TV, Android Auto, or Android Things, this section provides the guides and API reference you need.
The Android Support Library offers backward-compatible versions of a number of features, including others not built into the framework.
Check out these other resources for beginner and experienced Android developers.