Also function behavior and use cases in Kotlin - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to use the also function to print the number before returning it.

Kotlin

fun printNumber(num: Int): Int {
    return num.[1] {
        println("Number is: $it")
    }
}

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

Aapply

Brun

Calso

Dlet

Attempts:

3 left

💡 Hint

Common Mistakes

Using apply which returns the object but uses this instead of it.

Using let which returns the lambda result, not the original object.

The also function lets you perform an action with the object (here, num) and then returns the original object. This is perfect for printing and returning the same value.

2fill in blank

medium

Complete the code to add an element to the list and print the updated list using also.

Kotlin

val numbers = mutableListOf(1, 2, 3)
numbers.[1](4).also {
    println("Updated list: $numbers")
}

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

Aalso

Brun

Clet

Dapply

Attempts:

3 left

💡 Hint

Common Mistakes

Using apply which expects this and is used for configuring objects.

Using let which returns the lambda result, not the original object.

also is used here to perform an action (printing) after adding an element, while returning the original result of add.

3fill in blank

hard

Fix the error in the code by choosing the correct function to chain calls and print the object.

Kotlin

val text = "Hello"
val result = text.[1] {
    println(it)
}.uppercase()

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

Aapply

Balso

Crun

Dwith

Attempts:

3 left

💡 Hint

Common Mistakes

Using run which returns the lambda result, breaking the chain.

Using apply which uses this and may confuse chaining.

also returns the original object, so uppercase() can be called on the string. apply returns the object but uses this, run returns the lambda result, and with is not called as an extension.

4fill in blank

hard

Fill both blanks to create a mutable list, add an element, and print the list using also.

Kotlin

val list = mutableListOf(1, 2, 3).[1] {
    this.add(4)
}.[2] {
    println(it)
}

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

Aalso

Blet

Capply

Drun

Attempts:

3 left

💡 Hint

Common Mistakes

Using let which returns the lambda result, not the object.

Using run which returns the lambda result.

apply is used to add an element because it uses this and returns the object. Then also is used to print the list and return it.

5fill in blank

hard

Fill all three blanks to create a string, print it, convert to uppercase, and print again using also.

Kotlin

val message = "hello".[1] {
    println("Original: $it")
}.[2]().[3] {
    println("Uppercase: $it")
}

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

Aalso

Blet

Cuppercase

Dapply

Attempts:

3 left

💡 Hint

Common Mistakes

Using let which changes the return value and breaks chaining.

Using apply which uses this and is less clear here.

also is used to print the original string, then uppercase() converts it, and also prints the uppercase string. This keeps the original object flowing through the chain.

Practice

1. What does the also function do in Kotlin?

easy

A. Runs extra code on an object and returns the original object

B. Transforms the object and returns a new one

C. Stops the execution of the program

D. Creates a copy of the object

Solution

1. Step 1: Understand the purpose of also

   The also function is used to run some extra code on an object without changing it.

2. Step 2: Check the return value of also

   It returns the original object, not a transformed copy.

3. Final Answer:

   Runs extra code on an object and returns the original object -> Option A

4. Quick Check:

   also returns original object [OK]

Hint: Remember: also returns the original object unchanged [OK]

Common Mistakes:

• Thinking it returns a transformed object
• Confusing it with map or let
• Assuming it stops program execution

2. Which of the following is the correct syntax to use also with a variable num in Kotlin?

easy

A. also(num) { println(it) }

B. num.also -> { println(it) }

C. num.also println(it)

D. num.also { println(it) }

Solution

1. Step 1: Recall the syntax of also

   The also function is called on an object with a lambda block: object.also { ... }.

2. Step 2: Check each option for correct syntax

   num.also { println(it) } uses the correct dot call and lambda syntax. Options A, C, and D have syntax errors or wrong usage.

3. Final Answer:

   num.also { println(it) } -> Option D

4. Quick Check:

   Correct also syntax uses dot and lambda [OK]

Hint: Use dot and curly braces for lambda with also [OK]

Common Mistakes:

• Calling also as a standalone function
• Missing curly braces for lambda
• Using arrow without lambda properly

3. What is the output of this Kotlin code?

val list = mutableListOf(1, 2, 3)
val result = list.also { it.add(4) }
println(result)

medium

A. Compilation error

B. [1, 2, 3]

C. [1, 2, 3, 4]

D. Runtime exception

Solution

1. Step 1: Understand what also does here

   The also block adds 4 to the mutable list. Since the list is mutable, it changes the original list.

2. Step 2: Check the returned value

   also returns the original list, now modified with 4 added.

3. Final Answer:

   [1, 2, 3, 4] -> Option C

4. Quick Check:

   also returns original object after modification [OK]

Hint: also returns original object, so changes show in output [OK]

Common Mistakes:

• Thinking also returns a new list
• Ignoring that list is mutable
• Expecting original list without 4

4. Identify the error in this Kotlin code using also:

val text = "Hello"
text.also { it = it + " World" }
println(text)

medium

A. println syntax is incorrect

B. Cannot reassign 'it' inside also lambda

C. also cannot be used with strings

D. Missing return statement in also

Solution

1. Step 1: Analyze the lambda parameter 'it'

   In also, 'it' is a val (read-only), so you cannot reassign it inside the lambda.

2. Step 2: Check the code for reassignment

   The code tries to do it = it + " World", which is illegal and causes a compilation error.

3. Final Answer:

   Cannot reassign 'it' inside also lambda -> Option B

4. Quick Check:

   Lambda parameter 'it' is read-only [OK]

Hint: Remember: 'it' in also lambda is read-only [OK]

Common Mistakes:

• Trying to reassign 'it' inside lambda
• Confusing also with let for transformations
• Ignoring immutability of lambda parameters

5. Given a list of user names, how can you use also to log each name while returning the original list unchanged?

val users = listOf("Alice", "Bob", "Carol")
// Insert code here
println(users)

hard

A. users.also { it.forEach { name -> println(name) } }

B. users.map { println(it) }

C. users.let { it.forEach { println(it) } }

D. users.forEach { println(it) }

Solution

1. Step 1: Understand the goal

   We want to log each name but keep the original list unchanged and returned.

2. Step 2: Check each option's behavior

   users.also { it.forEach { name -> println(name) } } uses also to run logging side effects and returns the original list. Options B and C return transformed or Unit types, and D returns Unit.

3. Final Answer:

   users.also { it.forEach { name -> println(name) } } -> Option A

4. Quick Check:

   also runs side effects and returns original object [OK]

Hint: Use also for side effects without changing the object [OK]

Common Mistakes:

• Using map which changes the list
• Using let which returns last lambda result
• Using forEach alone which returns Unit