Let function behavior and use cases in Kotlin - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Kotlin code using let?

Consider the following Kotlin code snippet. What will it print when run?

Kotlin

val name: String? = "Anna"
val result = name?.let { it.uppercase() } ?: "No name"
println(result)

A null

B anna

C No name

D ANNA

💡 Hint

Remember that let runs the block only if the variable is not null.

The variable 'name' is not null, so let runs and converts it to uppercase, printing 'ANNA'.

❓ Predict Output

intermediate

What does this Kotlin code print when using let with a nullable variable?

Analyze this Kotlin code and determine its output.

Kotlin

val number: Int? = null
val output = number?.let { it * 2 } ?: -1
println(output)

A 0

B -1

C null

D 2

💡 Hint

If the variable is null, let block does not run and the Elvis operator provides the default.

Since 'number' is null, let is skipped and the Elvis operator returns -1.

🔧 Debug

advanced

Why does this Kotlin code cause a compilation error?

Examine the code below and identify the reason for the compilation error.

Kotlin

val text: String? = "hello"
val length = text.let { it.length }
println(length)

A Because 'text' is nullable, 'it.length' causes a compilation error.

B Because 'let' requires a non-null receiver, 'text.let' is invalid.

C Because 'it' inside let is nullable, accessing 'length' without safe call causes error.

D Because 'println' cannot print nullable types directly.

💡 Hint

Consider the type of 'it' inside the let block when the receiver is nullable.

Inside let, 'it' is the nullable type String?, so accessing 'length' without safe call or null check causes error.

🧠 Conceptual

advanced

What is a common use case for Kotlin's let function?

Choose the best description of a typical use case for the let function in Kotlin.

A To execute a block only when a variable is not null and transform its value.

B To declare a new variable with a different type inside a function.

C To replace the need for loops by iterating over collections.

D To create an extension function that modifies the original object.

💡 Hint

Think about how let helps with null safety and chaining.

Let is often used to run code only if a variable is not null and to transform or use its value safely.

❓ Predict Output

expert

What is the output of this Kotlin code using nested let functions?

Analyze the following Kotlin code and determine what it prints.

Kotlin

val a: String? = "foo"
val b: String? = null
val result = a?.let { x -> b?.let { y -> "$x and $y" } } ?: "No result"
println(result)

A No result

B foo and

C foo and null

D foo and foo

💡 Hint

Remember that the inner let runs only if 'b' is not null.

Since 'b' is null, the inner let does not run, so the whole expression is null and Elvis operator returns 'No result'.