Chaining scope functions in Kotlin - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to chain two scope functions on the string.

Kotlin

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

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

Aalso

Blet

Capply

Drun

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'let' returns the block result, not the original object.

Using 'apply' changes the context but returns the object, but it expects 'this' as receiver.

The also function returns the original object after applying the block, allowing chaining.

2fill in blank

medium

Complete the code to chain let and run to transform and print a string.

Kotlin

val length = "kotlin".let {
    it.uppercase()
}.[1] {
    println(this)
    this.length
}

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

Arun

Bapply

Cwith

Dalso

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'also' returns the original object, not the block result.

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

The run function executes the block with this as the context and returns the block result.

3fill in blank

hard

Fix the error in chaining apply and let to modify and print a mutable list.

Kotlin

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

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

Aalso

Bapply

Crun

Dwith

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'also' returns the object but expects 'it' as context, which may confuse modification.

Using 'run' returns the block result, not the object.

apply returns the object after applying changes, allowing let to receive the updated list.

4fill in blank

hard

Fill both blanks to chain let and also to transform and print a string.

Kotlin

val result = "scope".[1] {
    it.uppercase()
}.[2] {
    println(it)
}

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

Alet

Balso

Capply

Drun

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'apply' instead of 'also' changes the context to 'this' which is not expected here.

Using 'run' returns the block result but changes context to 'this'.

let transforms the string and returns the result; also prints it and returns the original object.

5fill in blank

hard

Fill all three blanks to chain apply, let, and also to modify, transform, and print a list.

Kotlin

val size = mutableListOf(5, 6).[1] {
    add(7)
}.[2] {
    it.sum()
}.[3] {
    println(it)
}

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

Aapply

Blet

Calso

Drun

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'run' changes context to 'this' and returns block result, which may confuse the chain.

Mixing 'also' and 'apply' in wrong order breaks the expected return values.

apply modifies the list and returns it; let calculates the sum; also prints the sum and returns it.

Practice

1. What does chaining scope functions in Kotlin help you achieve?

easy

A. Perform multiple operations on one object without repeating its name

B. Create multiple objects at once

C. Write loops faster

D. Automatically convert types

Solution

1. Step 1: Understand the purpose of scope functions

   Scope functions let you run code blocks on an object, often returning the object or a result.

2. Step 2: Recognize chaining benefit

   Chaining lets you call many scope functions one after another on the same object without repeating its name.

3. Final Answer:

   Perform multiple operations on one object without repeating its name -> Option A

4. Quick Check:

   Chaining scope functions = clean, repeated operations [OK]

Hint: Chaining avoids repeating object names in multiple calls [OK]

Common Mistakes:

• Thinking chaining creates new objects
• Confusing chaining with loops
• Believing chaining changes data types automatically

2. Which of the following is the correct syntax to chain apply and also on an object obj?

easy

A. obj.apply { }.also { }

B. obj.apply() also()

C. apply(obj) { } also { }

D. obj.apply { } also { }

Solution

1. Step 1: Recall correct chaining syntax

   In Kotlin, scope functions are called with dot notation and lambda blocks inside curly braces.

2. Step 2: Check each option

   obj.apply { }.also { } uses correct dot chaining with braces. obj.apply() also() misses dots and braces. apply(obj) { } also { } uses wrong function call style. obj.apply { } also { } misses dot before also.

3. Final Answer:

   obj.apply { }.also { } -> Option A

4. Quick Check:

   Dot + braces = correct chaining syntax [OK]

Hint: Use dot and braces for each scope function call [OK]

Common Mistakes:

• Omitting dots between functions
• Using parentheses instead of braces for lambdas
• Calling scope functions like regular functions without object

3. What is the output of this Kotlin code?

val result = "hello".also { println(it.uppercase()) }.length
println(result)

medium

A. hello\n5

B. 5\nHELLO

C. HELLO\nhello

D. HELLO\n5

Solution

1. Step 1: Understand also behavior

   also runs the lambda with the object as it, prints uppercase "HELLO", then returns the original string "hello".

2. Step 2: Calculate result

   After also, length is called on "hello", which is 5. Then println(result) prints 5.

3. Final Answer:

   HELLO 5 -> Option D

4. Quick Check:

   also prints uppercase, length returns 5 [OK]

Hint: also returns original object, so length is on original string [OK]

Common Mistakes:

• Thinking also returns uppercase string
• Confusing print order
• Expecting length to be printed before uppercase

4. Find the error in this Kotlin code chaining scope functions:

val text = "kotlin"
text.let { it.uppercase() }.apply { println(this) }

medium

A. apply cannot be called after let because let returns a different type

B. Missing lambda braces in apply

C. let does not return the original object, so apply prints wrong value

D. No error, code works fine

Solution

1. Step 1: Analyze let return value

   let returns the lambda result, here it.uppercase(), a new String "KOTLIN".

2. Step 2: Check apply receiver

   apply is called on the uppercase string, so this inside apply is "KOTLIN" and println(this) prints "KOTLIN".

3. Step 3: Identify the problem

   The original text is "kotlin", but apply prints the uppercase string, not the original. This may be unexpected if you want to print original.

4. Final Answer:

   let does not return the original object, so apply prints wrong value -> Option C

5. Quick Check:

   let returns lambda result, not original object [OK]

Hint: Remember let returns lambda result, not original object [OK]

Common Mistakes:

• Assuming let returns original object
• Thinking apply needs braces
• Believing no error exists

5. Given a mutable list val nums = mutableListOf(1, 2, 3), which chained scope function call correctly adds 4, prints the list, and returns the updated list?

hard

A. nums.let { it.add(4) }.also { println(it) }

B. nums.apply { add(4) }.also { println(it) }

C. nums.also { add(4) }.apply { println(this) }

D. nums.run { add(4); println(this) }

Solution

1. Step 1: Understand return values of scope functions

   apply returns the original object after running the block, also returns the original object too, let returns lambda result, run returns lambda result.

2. Step 2: Check each option

   nums.apply { add(4) }.also { println(it) } adds 4 inside apply, then prints list in also, returning the updated list. nums.let { it.add(4) }.also { println(it) }'s let returns Unit from add, so also prints Unit. nums.also { add(4) }.apply { println(this) } has syntax error ('add' unresolved in also block, needs it.add(4)). nums.run { add(4); println(this) } returns Unit from run.

3. Final Answer:

   nums.apply { add(4) }.also { println(it) } -> Option B

4. Quick Check:

   apply returns object, also prints it [OK]

Hint: Use apply to modify and also to print, both return original object [OK]

Common Mistakes:

• Using let which returns Unit from add
• Expecting run to return the list
• Confusing order of operations in chaining