Mastering ‘When’ in Kotlin: Tips, Tricks, and Best Practices

When it comes to Kotlin, the keyword “when” is one of the most useful constructs in the language. It’s like a Swiss Army knife for developers, with a variety of different use cases and applications.

🔎 What is “when” in Kotlin?

In Kotlin, “when” is a control flow construct that works like a switch statement in other languages. It allows you to match a value against a series of possible options, and execute different code based on which option matches.

Here’s an example of how “when” can be used to evaluate a variable and perform different actions:

val x = 1

when (x) {
    1 -> println("x is 1")
    2 -> println("x is 2")
    else -> println("x is neither 1 nor 2")
}

In this example, we use “when” to evaluate the value of the variable “x”. If “x” is 1, we print a message saying “x is 1”. If “x” is 2, we print a message saying “x is 2”. If “x” is neither 1 nor 2, we print a message saying “x is neither 1 nor 2”.

🤔 When to use “when” in Kotlin?

There are many situations where “when” can be useful in Kotlin. Here are a few examples:

✅ Matching against multiple values

One of the most common use cases for "when" is to match a value against multiple possible options. This is much more concise and readable than using a series of if/else statements.

when (x) {
    1, 2 -> println("x is either 1 or 2")
    in 3..10 -> println("x is between 3 and 10")
    else -> println("x is something else")
}

In this example, we use “when” to match the value of “x” against multiple options. We can use commas to match against multiple values at once, or ranges to match against a range of values.

✅ Checking for type

Another common use case for "when" is to check the type of an object. This is similar to using "instanceof" in other languages.

val obj: Any = "Hello, world!"

when (obj) {
    is String -> println("obj is a String with length ${obj.length}")
    is Int -> println("obj is an Int with value $obj")
    else -> println("obj is something else")
}

In this example, we use “when” to check the type of the “obj” variable. If “obj” is a String, we print a message with the length of the string. If “obj” is an Int, we print a message with the value of the integer. If “obj” is something else, we print a generic message.

✅ Using “when” as an expression

In Kotlin, "when" can also be used as an expression, which allows you to assign the result of the "when" block to a variable.

val result = when (x) {
    1 -> "x is 1"
    2 -> "x is 2"
    else -> "x is neither 1 nor 2"
}

println(result)

In this example, we use “when” as an expression to assign the result of the block to the “result” variable. We can then print the value of “result” to the console.

😂 Conclusion

In conclusion, “when” is an incredibly useful construct in Kotlin that can save you a lot of time and effort when writing code. Whether you’re matching against multiple

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