Kotlin Comments: A Comprehensive Guide

When developing in Kotlin, understanding how to write comments effectively is crucial to maintaining readable and maintainable code. Comments not only help others understand your code but also act as a reminder to your future self. In this blog post, we’ll dive into the types of comments in Kotlin, best practices for writing them, and how they can improve your codebase.

Types of Comments in Kotlin

Kotlin supports three types of comments:

1. Single-line comments
2. Multi-line comments
3. KDoc comments (for documentation)

1. Single-line Comments

Single-line comments in Kotlin are written using two forward slashes (//). Anything after the // on that line is considered a comment and will be ignored by the compiler.

val sum = 10 + 5 // This is a single-line comment

Single-line comments are ideal for brief descriptions or explanations of specific lines of code. They help clarify the purpose of variables, methods, or logic within a particular line.

Best Practice:

• Keep single-line comments short and to the point.
• Use them sparingly for explaining non-obvious logic or assumptions.

2. Multi-line Comments

Multi-line comments are written between /* and */. Everything between these markers is treated as a comment, regardless of how many lines it spans.

/*
 This is a multi-line comment.
 It can span multiple lines.
*/
val result = 10 * 5

Multi-line comments are perfect when you need to explain larger blocks of code or provide more context. They can also be nested in Kotlin, which is a useful feature when debugging sections of code.

Best Practice:

• Use multi-line comments for block-level explanations or when a complex section of code needs more clarity.
• Avoid over-commenting every line. Too many comments can clutter your code.

3. KDoc Comments (for Documentation)

Kotlin has built-in support for KDoc, a documentation system similar to Java’s Javadoc. KDoc comments are written using /** ... */ and are meant to provide documentation for classes, methods, and properties. KDoc comments can be extracted to generate external documentation, making them especially useful for library developers or larger projects.

/**
 * This function calculates the sum of two numbers.
 * @param a First number.
 * @param b Second number.
 * @return The sum of a and b.
 */
fun add(a: Int, b: Int): Int {
    return a + b
}

KDoc comments are more structured than standard multi-line comments and often include annotations like @param, @return, @throws, and others to describe function parameters, return values, and exceptions.

Best Practice:

• Use KDoc comments for public APIs, classes, and complex methods.
• Ensure that the documentation stays up-to-date as code changes.
• Include details about parameters, return values, and behavior.

Best Practices for Writing Comments

While comments are an essential part of any codebase, it’s important to write them thoughtfully. Here are some best practices to follow:

1. Comment Why, Not What

• Focus on explaining why something is done, not what the code does. The code itself should make the “what” clear.

   // Retrieve the current user from the database
   val user = database.getCurrentUser()

Instead of:

   // Get current user
   val user = database.getCurrentUser()

2. Keep Comments Up-to-Date

• Outdated comments can confuse developers. If the code changes, make sure the comments are updated to reflect those changes.

2. Avoid Over-Commenting

• Too many comments can clutter your code. If you need to comment every line of code, it may be a sign that the code itself is too complex. Aim to write self-explanatory code with meaningful variable and function names.

2. Use Comments for Non-Obvious Code

• If you’re using a complex algorithm or there’s some tricky logic, provide an explanation in a comment. For routine operations, comments are often unnecessary.

Conclusion

Comments are an essential part of writing clean, maintainable Kotlin code. By mastering single-line, multi-line, and KDoc comments, you’ll be able to document your code more effectively, making it easier for others (and yourself) to understand and maintain in the future. Remember to keep your comments clear, concise, and relevant to the context of your code.

Happy coding!