It keyword for single parameter in Kotlin - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of lambda using 'it' keyword

What is the output of this Kotlin code snippet using the 'it' keyword in a lambda?

Kotlin

val numbers = listOf(1, 2, 3, 4)
val doubled = numbers.map { it * 2 }
println(doubled)

A [1, 2, 3, 4]

B [2, 4, 6, 8]

C [3, 6, 9, 12]

D Compilation error

💡 Hint

The 'it' keyword refers to the single parameter of the lambda function.

The 'map' function applies the lambda to each element. 'it' is each element, so multiplying by 2 doubles each number.

❓ Predict Output

intermediate

Using 'it' in filter lambda

What will this Kotlin code print?

Kotlin

val words = listOf("apple", "banana", "cherry", "date")
val filtered = words.filter { it.length > 5 }
println(filtered)

A ["banana", "cherry"]

B ["apple", "date"]

C ["banana", "date"]

D []

💡 Hint

The 'it' keyword is the current element in the list during filtering.

The filter keeps words whose length is greater than 5. 'banana' and 'cherry' have length 6.

🔧 Debug

advanced

Identify the error with 'it' usage

What error does this Kotlin code produce?

Kotlin

val numbers = listOf(1, 2, 3)
numbers.forEach { println(it) }
numbers.forEach { val it = 5; println(it) }

A Compilation error: 'it' cannot be redeclared

B Runtime error: NullPointerException

C Compilation error: Val cannot be reassigned

D No error, prints 1 2 3 5 5 5

💡 Hint

You cannot redeclare 'it' inside the lambda.

The 'it' keyword is implicitly declared as the lambda parameter and cannot be redeclared inside the lambda body.

❓ Predict Output

advanced

Output of nested lambdas with 'it'

What is the output of this Kotlin code using nested lambdas with 'it'?

Kotlin

val list = listOf(1, 2, 3)
val result = list.map { it * 2 }.filter { it > 3 }
println(result)

A [2, 4, 6]

B [1, 2, 3]

C [4, 6]

D Compilation error due to ambiguous 'it'

💡 Hint

Each lambda has its own 'it' referring to the current element in that lambda.

The first lambda doubles each number: [2,4,6]. The second lambda filters numbers greater than 3: [4,6].

🧠 Conceptual

expert

Understanding 'it' scope in Kotlin lambdas

Consider this Kotlin code snippet. What is the value of 'result' after execution?

Kotlin

val result = listOf(1, 2, 3).fold(0) { acc, it -> acc + it }

A Compilation error: 'it' cannot be used with two parameters

B 0

C 3

D 6

💡 Hint

In fold, the lambda has two parameters, so 'it' is not used implicitly.

The fold function sums all elements starting from 0. The lambda uses 'acc' and 'it' explicitly, so 'it' is the current element.