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💬 Kotlin – Comments: Writing Clear and Maintainable Code

🧲 Introduction – Why Use Comments in Kotlin?

Comments are a fundamental part of writing clean, readable, and maintainable code. In Kotlin, comments help explain logic, disable code temporarily, or annotate sections for collaboration. Kotlin supports both single-line and multi-line comments, just like Java, making it easy for developers to document and debug efficiently.

🎯 In this guide, you’ll learn:

Types of comments in Kotlin and their syntax
How to use comments effectively for code documentation
Best practices for writing helpful comments
Common mistakes and when not to use comments

🧾 Types of Comments in Kotlin

Kotlin supports two types of comments:

Type	Syntax Example	Use Case
🟢 Single-Line	`// This is a single-line comment`	Quick notes or inline hints
🟦 Multi-Line	`/* This is a multi-line comment */`	Explaining code blocks or disabling sections

✅ Single-Line Comments

Use // to write brief notes on the same or separate line.

fun main() {
    val score = 95 // Declares a score variable
    println("Score: $score") // Output the score
}

🟢 Best for:

Documenting logic inline
Temporarily disabling one line
Quick reminders

✅ Multi-Line Comments

Use /* ... */ to span comments across multiple lines.

fun main() {
    /* This function prints
       a welcome message
       using Kotlin syntax */
    println("Welcome to Kotlin!")
}

🟢 Best for:

Block-level documentation
Temporarily disabling multiple lines
Team annotations or TODOs

📌 Nested Comments in Kotlin

Unlike Java, Kotlin supports nested block comments:

/* Outer comment
    /* Nested comment */
   End of outer comment */

✅ This is helpful when you need to comment out large code sections that may already contain comments.

📘 Commenting Out Code

You can disable code during testing using comments:

// val isActive = true
// println("User is active")

Or:

/*
val user = "Admin"
val role = "Editor"
println("$user is a $role")
*/

⚠️ Tip: Avoid leaving commented-out code in production unless it’s for future reference or debugging.

✍️ Best Practices for Writing Comments

Practice	Example
✅ Explain why, not what	`// Reversing list for UI order`
✅ Keep comments up to date	Update them when logic changes
✅ Avoid redundant comments	Don’t state the obvious
✅ Use TODO/FIXME annotations	`// TODO: Optimize loop condition`

🚫 Common Mistakes with Comments

❌ Mistake	✅ Better Approach
`// Incrementing x by 1` after `x++`	`// Ensure x doesn't exceed max limit`
Too many comments for obvious code	Comment only complex logic
Outdated comment misleading logic	Always sync comment with code

📌 Summary – Recap & Next Steps

Kotlin supports both single-line and multi-line comments, including nested ones, to help you write better-documented and maintainable code. Use them wisely to enhance collaboration and future-proof your projects.

🔍 Key Takeaways:

Use // for single-line and /* */ for multi-line comments.
Kotlin allows nested multi-line comments.
Comments should clarify logic, not restate code.
Use TODO and FIXME for tracking issues and improvements.

⚙️ Practical Use:
Use comments during development, code reviews, debugging, or while collaborating on projects—especially for explaining why something is done.

❓ FAQs – Kotlin Comments

❓ Does Kotlin support nested comments?
✅ Yes. Kotlin allows nesting of multi-line comments using /* /* ... */ */, unlike Java.

❓ What are TODO comments used for in Kotlin?
✅ TODO() is a special function in Kotlin that throws NotImplementedError.

fun futureFeature() = TODO("Not implemented yet")

❓ Should I comment every line of code?
✅ No. Comment only complex logic or decisions, not trivial assignments or obvious code.

❓ Can comments affect program output?
✅ No. Comments are ignored by the Kotlin compiler and have no effect on output or performance.

❓ How to quickly comment/uncomment in IDE?
✅ In IntelliJ/Android Studio, use Ctrl + / (Windows/Linux) or Cmd + / (Mac) for toggling single-line comments.

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