With 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 with function?

Consider the following Kotlin code snippet using the with function. What will be printed when this code runs?

Kotlin

data class Person(var name: String, var age: Int)

fun main() {
    val person = Person("Alice", 30)
    val result = with(person) {
        age += 1
        "${name} is now $age years old"
    }
    println(result)
}

A Compilation error due to string interpolation

B Alice is now 30 years old

C Alice is now 31 years old

D Runtime error: Unresolved reference

💡 Hint

Remember that with allows you to access the object's members directly and the last expression is returned.

The with function takes person as its receiver. Inside the block, age is incremented by 1, so it becomes 31. The last expression is a string that uses the updated age and name. This string is returned and printed.

🧠 Conceptual

intermediate

What is the main difference between with and apply in Kotlin?

Choose the option that correctly describes the key difference between with and apply functions in Kotlin.

A <code>with</code> returns the lambda result, <code>apply</code> returns the receiver object

B <code>with</code> returns the receiver object, <code>apply</code> returns the lambda result

C Both <code>with</code> and <code>apply</code> return the receiver object

D Both <code>with</code> and <code>apply</code> return the lambda result

💡 Hint

Think about what each function returns after executing the block.

with executes the block with the receiver as context and returns the last expression of the block (lambda result). apply executes the block with the receiver as context but returns the receiver object itself.

🔧 Debug

advanced

Why does this Kotlin code using with function cause a compilation error?

Examine the code below. It tries to use with on a nullable String. Why does it fail to compile?

Kotlin

fun main() {
    val text: String? = null
    with(text) {
        println(length)
    }
}

A The println statement has a syntax error

B Cannot call with on a nullable receiver without safe call operator

C The length property does not exist on String

D with requires a lambda with receiver, but none is provided

💡 Hint

Consider how Kotlin handles nullable types and scope functions.

The variable text is nullable. Calling with(text) without a safe call operator ?. causes a compilation error because with expects a non-null receiver. You must use text?.let { with(it) { ... } } or check for null before calling with.

❓ Predict Output

advanced

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

Analyze the following Kotlin code with nested with calls. What will it print?

Kotlin

data class Address(var city: String, var zip: String)

data class User(var name: String, var address: Address)

fun main() {
    val user = User("Bob", Address("NYC", "10001"))
    val result = with(user) {
        with(address) {
            "${[e-mail]} lives in $city with zip $zip"
        }
    }
    println(result)
}

A Runtime error: Unresolved reference to name

B Compilation error due to nested with

C Bob lives in with zip 10001

D Bob lives in NYC with zip 10001

💡 Hint

Remember that nested with blocks can access outer variables if referenced properly.

The outer with(user) sets the context to user. Inside, the inner with(address) sets the context to address. The string uses name from the outer scope and city, zip from the inner scope. This prints the full sentence correctly.

🧠 Conceptual

expert

Which statement about Kotlin's with function is TRUE?

Select the correct statement about the behavior and use cases of Kotlin's with function.

A <code>with</code> can be used to execute multiple operations on an object and returns the last expression result, but it is not an extension function.

B <code>with</code> is an extension function on any object and returns the object itself after executing the block.

C <code>with</code> requires the receiver object to be nullable and safely unwraps it inside the block.

D <code>with</code> is used to create new objects and always returns a new instance.

💡 Hint

Think about the signature and return type of with.

with is a regular function (not an extension) that takes the receiver object as an argument and executes the block with that receiver as context. It returns the last expression of the block, not the receiver object. It does not require the receiver to be nullable and does not create new objects.