Comments and documentation markup in Swift

Introduction

Comments help explain your code so others (and you) can understand it later. Documentation markup creates helpful notes that tools can show nicely.

When you want to explain why a piece of code exists.

When you want to remind yourself what a function does.

When you want to create clear instructions for others using your code.

When you want to add notes that show up in code completion or documentation tools.

When you want to temporarily disable code without deleting it.

Syntax

Swift

// This is a single-line comment
/* This is a
   multi-line comment */
/// This is a documentation comment for a function
/**
 This is a multi-line documentation comment
 for describing a function or type
*/

Single-line comments start with // and go to the end of the line.

Multi-line comments start with /* and end with */. They can span many lines.

Examples

A simple single-line comment before a print statement.

Swift

// This prints a greeting
print("Hello")

A multi-line comment that can explain more details.

Swift

/*
 This is a longer comment
 that explains multiple lines
*/
print("Hi")

A documentation comment that describes what the function does. Tools can show this info.

Swift

/// Adds two numbers and returns the result
func add(_ a: Int, _ b: Int) -> Int {
    return a + b
}

A multi-line documentation comment with parameters and return description.

Swift

/**
 Calculates the area of a rectangle.
 - Parameters:
   - width: The width of the rectangle.
   - height: The height of the rectangle.
 - Returns: The area as an Int.
*/
func area(width: Int, height: Int) -> Int {
    return width * height
}

Sample Program

This program shows how to use documentation comments to describe a function and regular comments inside the function. It then calls the function and prints the greeting.

Swift

/// Greets the user by name
/// - Parameter name: The name of the user
/// - Returns: A greeting string
func greet(name: String) -> String {
    // Create the greeting message
    let message = "Hello, \(name)!"
    return message
}

// Call the function and print the result
print(greet(name: "Alice"))

Important Notes

Use comments to explain why something is done, not just what the code does.

Keep comments short and clear to avoid confusion.

Documentation comments (/// or /** */) help tools generate helpful guides and autocomplete info.

Summary

Comments make code easier to understand for you and others.

Use single-line (//) for short notes and multi-line (/* */) for longer explanations.

Documentation comments (/// or /** */) describe functions and types for tools and users.

Practice

1. What is the main purpose of comments in Swift code?

easy

A. To create new variables

B. To make the code run faster

C. To explain the code for better understanding

D. To store user data

Solution

1. Step 1: Understand what comments do

   Comments are notes in the code that do not affect how the program runs but help explain what the code does.

2. Step 2: Identify the purpose of comments

   Comments make the code easier to read and understand for yourself and others who read the code later.

3. Final Answer:

   To explain the code for better understanding -> Option C

4. Quick Check:

   Comments explain code [OK]

Hint: Comments explain code, not run it or store data [OK]

Common Mistakes:

• Thinking comments speed up code
• Confusing comments with variables
• Using comments to store data

2. Which of the following is the correct syntax for a single-line comment in Swift?

easy

A. # This is a comment

B. /* This is a comment */

C.

D. // This is a comment

Solution

1. Step 1: Recall Swift comment syntax

   Swift uses // for single-line comments and /* */ for multi-line comments.

2. Step 2: Match the correct syntax

   // This is a comment uses // which is the correct single-line comment syntax in Swift.

3. Final Answer:

   // This is a comment -> Option D

4. Quick Check:

   Single-line comment = // [OK]

Hint: Single-line comments start with // in Swift [OK]

Common Mistakes:

• Using /* */ for single-line comments
• Using HTML style comments
• Using # which is not a comment in Swift

3. What will the following Swift code output?

/// Adds two numbers
func add(_ a: Int, _ b: Int) -> Int {
    return a + b
}
print(add(3, 4))

medium

A. 7

B. add(3, 4)

C. /// Adds two numbers

D. Error: Unexpected documentation comment

Solution

1. Step 1: Understand documentation comments effect

   The line starting with /// is a documentation comment and does not affect the code execution.

2. Step 2: Execute the function call

   The function add returns the sum of 3 and 4, which is 7, and print outputs it.

3. Final Answer:

   7 -> Option A

4. Quick Check:

   Documentation comment ignored, output = 7 [OK]

Hint: Documentation comments don't change output, only explain [OK]

Common Mistakes:

• Thinking documentation comments print text
• Expecting error from documentation comments
• Confusing comments with code

4. Identify the error in this Swift code snippet:

/* This is a multi-line comment
func greet() {
    print("Hello")
}
// Missing closing comment delimiter

medium

A. Using // inside multi-line comment is invalid

B. Missing closing */ for multi-line comment

C. Function greet() is not declared properly

D. print statement syntax error

Solution

1. Step 1: Check multi-line comment syntax

   Multi-line comments start with /* and must end with */ to close properly.

2. Step 2: Identify missing closing delimiter

   The code has /* but no closing */, so the comment never ends, causing a syntax error.

3. Final Answer:

   Missing closing */ for multi-line comment -> Option B

4. Quick Check:

   Multi-line comment must close with */ [OK]

Hint: Multi-line comments need /* and */ to open and close [OK]

Common Mistakes:

• Ignoring missing closing comment delimiter
• Thinking // can't be inside multi-line comments
• Assuming function syntax is wrong

5. You want to document a Swift function so that Xcode shows its description and parameters clearly. Which comment style should you use?

func multiply(_ x: Int, _ y: Int) -> Int {
    return x * y
}

hard

A. /// Multiplies two numbers
/// - Parameters:
/// - x: The first number
/// - y: The second number
/// - Returns: The product of x and y

B. /* Multiplies two numbers */

C. // This function multiplies two numbers

D.

Solution

1. Step 1: Understand documentation comment usage

   Documentation comments in Swift use /// and special markup to describe functions and parameters for tools like Xcode.

2. Step 2: Identify the detailed documentation style

   /// Multiplies two numbers /// - Parameters: /// - x: The first number /// - y: The second number /// - Returns: The product of x and y uses /// with - Parameters and - Returns tags, which is the correct way to document for Xcode's quick help.

3. Final Answer:

   /// Multiplies two numbers /// - Parameters: /// - x: The first number /// - y: The second number /// - Returns: The product of x and y -> Option A

4. Quick Check:

   Use /// with parameter tags for documentation [OK]

Hint: Use /// with - Parameters and - Returns for Xcode docs [OK]

Common Mistakes:

• Using single-line or multi-line comments without markup
• Using HTML style comments
• Not including parameter descriptions