Why scope functions reduce boilerplate in Kotlin - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create an instance of a StringBuilder and append text using a scope function.

Kotlin

val result = StringBuilder().[1] {
    append("Hello")
    append(" World")
}.toString()

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

Aapply

Balso

Crun

Dlet

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'let' returns the lambda result, not the object itself.

The apply function allows you to configure an object within its scope and returns the object itself, reducing boilerplate when initializing.

2fill in blank

medium

Complete the code to safely access the length of a nullable string using a scope function.

Kotlin

val length = nullableString?.[1] {
    length
} ?: 0

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

Aapply

Blet

Crun

Dalso

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'apply' returns the object, not the lambda result.

The let function is useful for executing code only if the object is not null and returns the lambda result.

3fill in blank

hard

Fix the error in the code by choosing the correct scope function to execute a block and return its result.

Kotlin

val result = "Hello".[1] {
    this.length
}

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

Aapply

Balso

Cwith

Drun

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'apply' returns the object, not the lambda result.

The run function executes the block with the object as receiver and returns the lambda result, suitable here to get the length.

4fill in blank

hard

Fill both blanks to create a mutable list and add elements using scope functions.

Kotlin

val list = mutableListOf<Int>().[1] {
    add(1)
    add(2)
}.[2] {
    println("List size: $size")
}

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

Aapply

Blet

Calso

Drun

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'let' for the first blank returns the lambda result, not the list.

apply is used to configure the list by adding elements, returning the list itself. also is used to perform an additional action (printing) without changing the list.

5fill in blank

hard

Fill all three blanks to filter a list and create a map of word lengths using scope functions.

Kotlin

val words = listOf("apple", "banana", "cherry")
val lengths = words.filter { it.length [1] 5 }.[2] {
    associateWith { it.length [3] 0 }
}

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

A>

Bapply

C?:

Dlet

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'apply' instead of 'let' for the second blank returns the object, not the transformed result.

The filter uses > to select words longer than 5. The let function is used to transform the filtered list. The Elvis operator ?: provides a default value if length is null (though length is non-null here, it's used illustratively).