How to Use Named Parameters in Kotlin: Simple Guide

In Kotlin, you use named parameters by specifying the parameter name followed by an equals sign and the value when calling a function, like functionName(paramName = value). This makes your code clearer and lets you pass arguments in any order.

Syntax

Named parameters let you specify the name of the argument when calling a function. This helps make your code easier to read and allows you to pass arguments in any order.

The syntax is: functionName(parameterName = value).

Each named parameter consists of the parameter's name, an equals sign, and the value you want to pass.

kotlin

fun greet(name: String, age: Int) {
    println("Hello, $name! You are $age years old.")
}

greet(name = "Alice", age = 30)

Output

Hello, Alice! You are 30 years old.

Example

This example shows how to use named parameters to call a function with multiple arguments. You can pass the arguments in any order by naming them.

kotlin

fun bookDetails(title: String, author: String, year: Int) {
    println("Title: $title")
    println("Author: $author")
    println("Year: $year")
}

// Calling with named parameters in different order
bookDetails(year = 2021, title = "Kotlin Basics", author = "John Doe")

Output

Title: Kotlin Basics
Author: John Doe
Year: 2021

Common Pitfalls

One common mistake is mixing positional and named arguments incorrectly. In Kotlin, all positional arguments must come before any named arguments.

Also, using named parameters with default values can help avoid passing unnecessary arguments.

kotlin

fun printInfo(name: String, age: Int, city: String = "Unknown") {
    println("Name: $name, Age: $age, City: $city")
}

// Correct usage: positional first, then named
printInfo("Bob", age = 25)

// Incorrect usage: named before positional (will cause error)
// printInfo(age = 25, "Bob")

Output

Name: Bob, Age: 25, City: Unknown

Quick Reference

• Use parameterName = value to pass named parameters.
• Positional arguments must come before named arguments.
• Named parameters improve readability and allow flexible argument order.
• Combine named parameters with default values to simplify calls.

Key Takeaways

Use named parameters by specifying parameterName = value when calling functions.

Named parameters let you pass arguments in any order for clearer code.

Always put positional arguments before named arguments to avoid errors.

Combine named parameters with default values to simplify function calls.

Named parameters improve code readability and reduce mistakes.