Result type for functional error handling in Kotlin - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a successful Result with value 42.

Kotlin

val result: Result<Int> = Result.[1](42)

Drag options to blanks, or click blank then click option'

Aof

BrunCatching

Csuccess

Dfailure

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'failure' instead of 'success' creates an error Result.

Using 'runCatching' requires a lambda, not a direct value.

Use Result.success(value) to create a successful Result wrapping the value.

2fill in blank

medium

Complete the code to create a failed Result with an exception.

Kotlin

val errorResult: Result<Int> = Result.[1](IllegalArgumentException("Invalid input"))

Drag options to blanks, or click blank then click option'

Aof

BrunCatching

Csuccess

Dfailure

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'success' instead of 'failure' creates a success Result.

Using 'runCatching' requires a lambda, not an exception directly.

Use Result.failure(exception) to create a failed Result wrapping the exception.

3fill in blank

hard

Fix the error in the code to catch exceptions and return a Result.

Kotlin

val result = Result.[1] { 10 / 0 }

Drag options to blanks, or click blank then click option'

ArunCatching

Bsuccess

Cfailure

Dof

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'success' or 'failure' directly does not execute the lambda.

Using 'of' is not a standard Result function.

runCatching runs the lambda and catches exceptions, returning a Result.

4fill in blank

hard

Fill both blanks to create a map operation on a Result.

Kotlin

val mapped = result.[1] { it [2] 2 }

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Amap

B*

C+

Dfold

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'fold' instead of 'map' changes the Result type.

Using '+' instead of '*' changes the operation.

Use map to transform the success value, and * to multiply by 2.

5fill in blank

hard

Fill all three blanks to handle success and failure with fold.

Kotlin

val message = result.[1](
  onSuccess = { "Success: " + it.toString() },
  onFailure = { [2] -> "Error: " + [3].message }
)

Drag options to blanks, or click blank then click option'

Afold

Be

Dmap

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'map' instead of 'fold' only handles success.

Using different names for the failure parameter and usage causes errors.

fold handles both success and failure. The failure lambda parameter is named e to access the exception.

Practice

1. What does the Kotlin Result type represent in functional error handling?

easy

A. A special type of exception thrown during errors

B. An object that holds either a success value or a failure exception

C. A function that always returns a Boolean

D. A list of all errors encountered during execution

Solution

1. Step 1: Understand the purpose of Result type

   The Result type is designed to wrap either a successful outcome or an error, making error handling explicit and functional.

2. Step 2: Identify what Result holds

   Result holds either a success value or a failure exception, not a list or a Boolean or an exception thrown directly.

3. Final Answer:

   An object that holds either a success value or a failure exception -> Option B

4. Quick Check:

   Result = success or failure [OK]

Hint: Result always wraps success or failure, not exceptions thrown [OK]

Common Mistakes:

• Thinking Result is an exception type
• Confusing Result with Boolean return
• Assuming Result holds multiple errors

2. Which of the following is the correct way to create a successful Result object in Kotlin?

easy

A. Result.makeSuccess(value)

B. Result.ofSuccess(value)

C. Result.createSuccess(value)

D. Result.success(value)

Solution

1. Step 1: Recall the Kotlin Result API

   Kotlin provides Result.success(value) to create a successful Result wrapping the value.

2. Step 2: Check method names

   Only Result.success is the correct and existing method; others are invalid.

3. Final Answer:

   Result.success(value) -> Option D

4. Quick Check:

   Use Result.success() to wrap success [OK]

Hint: Use Result.success() to wrap success values [OK]

Common Mistakes:

• Using non-existent methods like Result.ofSuccess
• Confusing with factory methods
• Trying to create Result with constructors

3. What will be the output of this Kotlin code?

val result = runCatching { 10 / 0 }
result.onSuccess { println("Success: $it") }
result.onFailure { println("Failure: ${it.message}") }

medium

A. Failure: / by zero

B. Success: 0

C. No output

D. RuntimeException thrown

Solution

1. Step 1: Understand runCatching behavior

   runCatching executes the block and catches exceptions, wrapping them in Result.failure.

2. Step 2: Analyze division by zero

   10 / 0 throws an ArithmeticException with message "/ by zero" which is caught and triggers onFailure.

3. Final Answer:

   Failure: / by zero -> Option A

4. Quick Check:

   Exception caught triggers onFailure [OK]

Hint: runCatching catches exceptions and calls onFailure [OK]

Common Mistakes:

• Expecting program to crash with exception
• Thinking onSuccess runs despite error
• Ignoring exception message in output

4. Identify the error in this Kotlin code using Result for error handling:

fun divide(a: Int, b: Int): Result<Int> {
    return try {
        Result.success(a / b)
    } catch (e: Exception) {
        Result.failure(e)
    }
}

val result = divide(10, 0)
result.onSuccess { println("Result: $it") }
      .onFailure { println("Error: ${it.message}") }

medium

A. Cannot chain onSuccess and onFailure directly on Result

B. Should catch ArithmeticException instead of Exception

C. Result.failure should not be used inside catch block

D. No error, code works correctly

Solution

1. Step 1: Check chaining onSuccess and onFailure

   In Kotlin, onSuccess and onFailure are extension functions returning Unit, so chaining them directly causes a compile error.

2. Step 2: Verify other parts

   Try-catch with Result.success and Result.failure is correct; catching Exception is acceptable; Result.failure is valid.

3. Final Answer:

   Cannot chain onSuccess and onFailure directly on Result -> Option A

4. Quick Check:

   onSuccess and onFailure return Unit, no chaining [OK]

Hint: onSuccess/onFailure return Unit, cannot chain calls [OK]

Common Mistakes:

• Trying to chain onSuccess and onFailure
• Thinking catch block must catch ArithmeticException only
• Misusing Result.failure inside catch

5. You want to write a Kotlin function that returns a Result wrapping the parsed integer from a string, or a failure if parsing fails. Which implementation correctly uses Result for this purpose?

hard

A. fun parseInt(str: String): Result<Int> = Result.failure(NumberFormatException())

B. fun parseInt(str: String): Result<Int> = Result.success(str.toIntOrNull() ?: throw NumberFormatException())

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

D. fun parseInt(str: String): Int = str.toIntOrNull() ?: -1

Solution

1. Step 1: Understand the goal

   The function should return Result wrapping success if parsing works, or failure if it throws NumberFormatException.

2. Step 2: Analyze each option

   fun parseInt(str: String): Result<Int> = try { Result.success(str.toInt()) } catch (e: NumberFormatException) { Result.failure(e) } uses try-catch to wrap success or failure correctly. fun parseInt(str: String): Result<Int> = Result.success(str.toIntOrNull() ?: throw NumberFormatException()) throws exception outside Result.failure, breaking functional style. fun parseInt(str: String): Result<Int> = Result.failure(NumberFormatException()) always returns failure, ignoring input. fun parseInt(str: String): Int = str.toIntOrNull() ?: -1 returns Int, not Result.

3. Final Answer:

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

4. Quick Check:

   Try-catch with Result.success/failure wraps parsing safely [OK]

Hint: Use try-catch with Result.success and Result.failure for safe parsing [OK]

Common Mistakes:

• Throwing exceptions instead of wrapping in Result.failure
• Returning plain Int instead of Result<Int>
• Always returning failure ignoring input