Smart casts in when and if in Kotlin - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if the variable is a String using is.

Kotlin

fun checkType(x: Any) {
    if (x [1] String) {
        println("It's a string of length ${x.length}")
    }
}

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

A==

Bas

Cis

Din

Attempts:

3 left

💡 Hint

Common Mistakes

Using '==' instead of 'is' for type checking.

Using 'as' which is for casting, not checking.

In Kotlin, is checks if a variable is of a certain type and smart casts it inside the block.

2fill in blank

medium

Complete the when expression to smart cast obj to Int.

Kotlin

fun describe(obj: Any): String = when (obj) {
    is [1] -> "Integer with value $obj"
    else -> "Unknown"
}

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

AInt

BString

CDouble

DBoolean

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing String or Double instead of Int.

Forgetting that is is needed for smart cast.

The when expression smart casts obj to Int when using is Int.

3fill in blank

hard

Fix the error by completing the if condition to smart cast value to String.

Kotlin

fun printLength(value: Any) {
    if (value [1] String) {
        println(value.length)
    }
}

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

Ais

B==

Cas

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '==' which compares values, not types.

Using 'as' which is unsafe casting.

Using is smart casts value to String inside the if block, allowing access to length.

4fill in blank

hard

Fill both blanks to create a dictionary comprehension that includes only strings longer than 3 characters.

Kotlin

val words = listOf("cat", "house", "dog", "elephant")
val result = words.associateWith { it.length }.filter { it.key [1] 3 && it.key [2] String }
println(result)

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A>

Bis

C<

D==

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' instead of '>' for length comparison.

Using '==' instead of 'is' for type checking.

The filter keeps entries where the key is a String and its length is greater than 3.

5fill in blank

hard

Fill all three blanks to create a when expression that smart casts and returns descriptions.

Kotlin

fun describeInput(input: Any): String = when {
    input [1] String -> "String of length ${input.length}"
    input [2] Int -> "Integer value $input"
    input [3] Boolean -> "Boolean value $input"
    else -> "Unknown type"
}

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

Ais

B==

C!=

Das

Attempts:

3 left

💡 Hint

Common Mistakes

Using '==' or '!=' instead of 'is' for type checking.

Using 'as' which casts but can throw exceptions.

Using is in when smart casts input to the checked type inside each branch.