Documentation in Swift: How to Write Code That Speaks for Itself

Why Documentation is a Developer's Superpower

Imagine: you open someone else's Swift project six months after it was written. The code works, but understanding why the author did it this way and not another is impossible. No comments, variable names like a1, temp2. Sound familiar?

Good documentation is not just politeness to your future self. It's a tool that saves hours of debugging, accelerates onboarding for new developers, and turns chaos into a coherent system. In this article, we'll break down the best practices for documenting Swift code, from basic comments to advanced DocC.

Basics: From Simple Comments to Meaningful Descriptions

//, /// and /* */ — When to Use What

Swift has three types of comments, each for its own purpose:

• Single-line // — for quick notes, TODOs, or temporarily disabling code. Don't overuse them: if a comment explains the obvious, it's unnecessary.
• Multi-line /* */ — for blocks of explanation or disabling entire sections of code during debugging.
• Documentation /// — this is your main tool. Xcode automatically picks them up and displays them in Quick Help.

/// Calculates the area of a circle given its radius./// - Parameter radius: The radius of the circle in meters./// - Returns: The area in square meters./// - Throws: `InvalidInputError.negativeRadius` if radius < 0.func areaOfCircle(radius: Double) throws -> Double {    guard radius >= 0 else {        throw InvalidInputError.negativeRadius    }    return Double.pi * radius * radius}

Bad vs Good Comment

Compare the two approaches:

// BAD: Obvious comment// Increment the counter by 1counter += 1

// GOOD: Explain the "why"// Using increment because this is a performance-critical// section, and the ++ operator is deprecated in Swiftcounter += 1

The golden rule: a comment should answer the question "why", not "what" the code does. The code itself should be readable so that the "what" is clear without words.

DocC — Next-Generation Documentation

What is DocC and Why It's a Must-Have

With the release of Xcode 13, Apple introduced DocC (Documentation Compiler) — a tool that turns your /// comments into beautiful, interactive documentation right inside Xcode and on the web. No more PDF files and wiki pages that become outdated within a week.

How to Use DocC in a Project

1. Setup: In Xcode, select Product → Build Documentation. DocC will automatically collect all documented symbols.
2. Links within documentation: Use `` to link to other types:

/// Use ``NetworkManager`` to send requests./// See the article <doc:NetworkGuide> for more details.

3. Markdown capabilities: DocC supports headings, lists, tables, images, and even Mermaid diagrams:

/// # Algorithm Workflow/// 1. Check cache/// 2. If not found — request from server/// 3. Save the result

Creating Documentation for an Entire Module

Add a Documentation.docc file to the project root. Inside, a structure in Markdown:

// MyFramework.docc/MyFramework.md# ``MyFramework``

An asynchronous library for network operations.

## Topics

### Core Components- ``NetworkManager``- ``RequestBuilder``

### Extensions- <doc:CustomizingRequests>

Advanced Techniques: Writing Documentation That Gets Read

Structure by Roles

Not all code requires the same level of detail. Divide the docume