Result type for functional error handling in Kotlin - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Kotlin code using Result?

Consider this Kotlin code that uses Result to handle errors functionally. What will it print?

Kotlin

fun divide(a: Int, b: Int): Result<Int> =
    if (b == 0) Result.failure(ArithmeticException("Division by zero"))
    else Result.success(a / b)

fun main() {
    val result = divide(10, 0)
    println(result.getOrElse { _ -> -1 })
}

A Exception in thread "main" java.lang.ArithmeticException: Division by zero

B 0

C -1

D 10

💡 Hint

Look at how getOrElse works when the Result is a failure.

The divide function returns a failure Result when dividing by zero. The getOrElse method returns the success value or the default value if failure. Here, it returns -1 because division by zero fails.

❓ Predict Output

intermediate

What does this Kotlin code print when using Result.fold?

Given this Kotlin code using Result.fold, what will be printed?

Kotlin

fun parseNumber(str: String): Result<Int> =
    try {
        Result.success(str.toInt())
    } catch (e: NumberFormatException) {
        Result.failure(e)
    }

fun main() {
    val result = parseNumber("abc")
    val output = result.fold(
        onSuccess = { "Number: $it" },
        onFailure = { "Error: ${it.message}" }
    )
    println(output)
}

A Error: For input string: "abc"

B Number: abc

C Number: 0

D Exception in thread "main" java.lang.NumberFormatException: For input string: "abc"

💡 Hint

Think about what happens when toInt() fails and how fold handles success and failure.

The parseNumber function returns a failure Result because "abc" is not a valid integer. The fold method calls onFailure lambda, printing the error message.

❓ Predict Output

advanced

What is the output of this Kotlin code chaining Result operations?

Analyze this Kotlin code that chains Result operations with map and recover. What will it print?

Kotlin

fun riskyOperation(x: Int): Result<Int> =
    if (x > 0) Result.success(100 / x) else Result.failure(IllegalArgumentException("x must be positive"))

fun main() {
    val result = riskyOperation(0)
        .map { it * 2 }
        .recover<IllegalArgumentException> { _ -> 42 }
    println(result.getOrNull())
}

A 200

B 0

C Exception in thread "main" java.lang.IllegalArgumentException: x must be positive

D 42

💡 Hint

Check what recover does when the Result is a failure.

The riskyOperation returns a failure because x is 0. The map is skipped. The recover replaces the failure with success value 42. So getOrNull() returns 42.

❓ Predict Output

advanced

What error does this Kotlin code raise when accessing Result's value?

What error will this Kotlin code produce when run?

Kotlin

fun main() {
    val failureResult: Result<Int> = Result.failure(RuntimeException("Failed operation"))
    println(failureResult.getOrThrow())
}

A IllegalStateException

B RuntimeException: Failed operation

C NoSuchElementException

D NullPointerException

💡 Hint

Look at what getOrThrow() does when the Result is a failure.

The getOrThrow() method throws the exception stored in the failure Result. Here it throws the RuntimeException with message "Failed operation".

🧠 Conceptual

expert

How many items are in the resulting list after this Kotlin Result sequence?

Consider this Kotlin code that collects successful results from a list of Result values. How many items will be in the successes list?

Kotlin

fun main() {
    val results = listOf(
        Result.success(1),
        Result.failure(Exception("fail 1")),
        Result.success(2),
        Result.failure(Exception("fail 2")),
        Result.success(3)
    )
    val successes = results.mapNotNull { it.getOrNull() }
    println(successes.size)
}

A 3

B 2

C 5

D 0

💡 Hint

Remember that getOrNull() returns the value if success, or null if failure.

There are 3 successful Result objects (1, 2, 3). The mapNotNull collects only these values, so the list size is 3.