Examples of Kotlin When Expression

Introduction to Kotlin When Expressions

Kotlin’s when expression is a powerful control structure that allows you to execute different branches of code based on the value of a variable or expression. It serves as an alternative to the if-else statement, providing a more readable and organized way to handle multiple conditions. Below are three diverse, practical examples of Kotlin when expressions that demonstrate their effectiveness in real-world scenarios.

Example 1: Day of the Week Determination

This example illustrates how to use a when expression to determine the name of the day based on an integer input.

In this context, you might want to convert a numeric representation of a day (1 for Monday, 2 for Tuesday, etc.) into its corresponding name.

fun getDayName(day: Int): String {
    return when (day) {
        1 -> "Monday"
        2 -> "Tuesday"
        3 -> "Wednesday"
        4 -> "Thursday"
        5 -> "Friday"
        6 -> "Saturday"
        7 -> "Sunday"
        else -> "Invalid day"
    }
}

fun main() {
    println(getDayName(3))  // Output: Wednesday
}

In this example, the when expression evaluates the day parameter and returns the corresponding day name or an error message if the input is invalid.

Example 2: User Role Handling in an Application

In this example, we demonstrate how to use a when expression to assign user permissions based on their role in an application, such as Admin, User, or Guest.

This is particularly useful for applications that require different functionalities for various user types.

fun getUserPermissions(role: String): String {
    return when (role) {
        "Admin" -> "Full access to all resources"
        "User" -> "Access to standard resources"
        "Guest" -> "Limited access to public resources"
        else -> "Role not recognized"
    }
}

fun main() {
    println(getUserPermissions("Admin"))  // Output: Full access to all resources
}

Here, the when expression checks the role parameter and returns a string describing the permissions associated with that role. If the role is not recognized, it provides a fallback message.

Example 3: Evaluating Expression Values

This example shows how to use a when expression to evaluate a numerical score and categorize it into grades (e.g., A, B, C, etc.).

This type of evaluation is common in educational applications where student performance needs to be assessed.

fun getGrade(score: Int): String {
    return when {
        score >= 90 -> "A"
        score >= 80 -> "B"
        score >= 70 -> "C"
        score >= 60 -> "D"
        score < 60 -> "F"
        else -> "Invalid score"
    }
}

fun main() {
    println(getGrade(85))  // Output: B
}

In this case, the when expression checks ranges of scores without needing to specify the exact value, making it flexible for various grading systems. If the score is outside the usual range, an error message is returned.

These examples illustrate the versatility of Kotlin’s when expression, making it a valuable tool for developers looking to create clean and efficient code.