Data class copy and destructuring in Kotlin - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a copy of the data class instance with a new age.

Kotlin

val person2 = person.[1](age = 30)

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

Aclone

Bcopy

Cduplicate

DcopyOf

Attempts:

3 left

💡 Hint

Common Mistakes

Using clone() which is not available for Kotlin data classes.

Trying to use copyOf() which is not a data class function.

The copy() function is used to create a copy of a data class instance with some properties changed.

2fill in blank

medium

Complete the code to destructure the data class into variables.

Kotlin

val (name, [1]) = person

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

Aage

Bweight

Cheight

Daddress

Attempts:

3 left

💡 Hint

Common Mistakes

Using a property name not declared in the data class.

Mixing up the order of properties.

Data classes automatically provide componentN() functions for destructuring. The second property is 'age'.

3fill in blank

hard

Fix the error in the copy function call to change the name.

Kotlin

val person3 = person.[1](name = "Alice")

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

Acopy

Bduplicate

Cclone

DcopyOf

Attempts:

3 left

💡 Hint

Common Mistakes

Using clone() or copyOf() which are not valid for data classes.

Misspelling the function name.

The correct function to copy a data class with modifications is copy().

4fill in blank

hard

Fill both blanks to destructure the data class and print the values.

Kotlin

val ([1], [2]) = person
println("Name: $[1], Age: $[2]")

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

Aname

Bage

Cheight

Dweight

Attempts:

3 left

💡 Hint

Common Mistakes

Using properties not declared in the data class.

Mixing up the order of variables.

The first and second properties of the data class are 'name' and 'age', used for destructuring.

5fill in blank

hard

Fill all three blanks to copy the data class with a new name, destructure it, and print the values.

Kotlin

val person4 = person.[1](name = "Bob")
val ([2], [3]) = person4
println("Name: $[2], Age: $[3]")

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

Acopy

Bname

Cage

Dclone

Attempts:

3 left

💡 Hint

Common Mistakes

Using clone() instead of copy().

Mixing up variable names in destructuring.

Use copy() to create a new instance with a changed name, then destructure into name and age variables.

Practice

1.

What does the copy() function do in a Kotlin data class?

easy

A. Changes the original object directly.

B. Deletes the original object and creates a new one.

C. Creates a new object with the same properties, optionally changing some.

D. Converts the object to a string representation.

Solution

1. Step 1: Understand the purpose of copy()

   The copy() function in Kotlin data classes creates a new instance with the same property values.

2. Step 2: Recognize optional property changes

   You can specify new values for some properties while copying, leaving others unchanged.

3. Final Answer:

   Creates a new object with the same properties, optionally changing some. -> Option C

4. Quick Check:

   copy() = new object with changes [OK]

Hint: Remember: copy() clones with optional changes [OK]

Common Mistakes:

• Thinking copy() modifies the original object
• Confusing copy() with toString()
• Assuming copy() deletes the original

2.

Which of the following is the correct syntax to copy a Kotlin data class Person and change only the age property?

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

easy

A. val newPerson = person.copy(age = 30)

B. val newPerson = person.copy(30)

C. val newPerson = copy(person, age = 30)

D. val newPerson = person.copy(name = "John")

Solution

1. Step 1: Recall the copy() syntax

   The copy() function uses named arguments to change specific properties.

2. Step 2: Identify correct usage

   Using person.copy(age = 30) changes only the age, keeping name same.

3. Final Answer:

   val newPerson = person.copy(age = 30) -> Option A

4. Quick Check:

   copy() uses named args for changes [OK]

Hint: Use named arguments inside copy() to change properties [OK]

Common Mistakes:

• Passing values without property names
• Using copy() as a standalone function
• Changing wrong property by mistake

3.

What is the output of this Kotlin code?

data class Point(val x: Int, val y: Int)

fun main() {
    val p1 = Point(5, 10)
    val (a, b) = p1
    val p2 = p1.copy(y = 20)
    println("a = $a, b = $b")
    println(p2)
}

medium

A. a = 5, b = 20
Point(x=5, y=10)

B. a = 5, b = 10
Point(x=5, y=20)

C. a = 10, b = 5
Point(x=5, y=20)

D. a = 5, b = 10
Point(x=5, y=10)

Solution

1. Step 1: Understand destructuring of p1

   Destructuring assigns a = p1.x = 5 and b = p1.y = 10.

2. Step 2: Understand copy() usage

   p2 is a copy of p1 with y changed to 20, so Point(x=5, y=20).

3. Final Answer:

   a = 5, b = 10 Point(x=5, y=20) -> Option B

4. Quick Check:

   Destructuring + copy() = expected values [OK]

Hint: Destructure original, copy with changed property [OK]

Common Mistakes:

• Mixing up destructured values
• Assuming copy changes original
• Printing wrong variable

4.

Find the error in this Kotlin code snippet:

data class User(val name: String, val age: Int)

fun main() {
    val user1 = User("Alice", 25)
    val (n, a) = user1.copy(age = 30)
    println("Name: $n, Age: $a")
}

medium

A. Variable names in destructuring must match property names.

B. Destructuring cannot be done on copy() result.

C. copy() requires all properties to be specified.

D. No error; code runs and prints updated age.

Solution

1. Step 1: Check copy() usage

   The copy() function is correctly called with age = 30.

2. Step 2: Check destructuring

   Destructuring works on the copy result, assigning n = "Alice" and a = 30.

3. Final Answer:

   No error; code runs and prints updated age. -> Option D

4. Quick Check:

   copy() + destructuring works fine [OK]

Hint: copy() returns data class instance usable for destructuring [OK]

Common Mistakes:

• Thinking destructuring fails on copy() result
• Believing copy() needs all properties
• Confusing variable names with property names

5.

Given this data class and list, how do you create a new list of Person objects with age increased by 1, using copy() and destructuring?

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

val people = listOf(Person("Tom", 20), Person("Sue", 25))

hard

A. people.map { it.copy(age = it.age + 1) }

B. people.forEach { it.copy(age = it.age + 1) }

C. people.copy { age += 1 }

D. people.map { (n, a) -> Person(n, a + 1) }

Solution

1. Step 1: Understand list transformation

   We want to create a new list with each person's age increased by 1.

2. Step 2: Use copy() inside map()

   Using map with it.copy(age = it.age + 1) creates new objects with updated age.

3. Final Answer:

   people.map { it.copy(age = it.age + 1) } -> Option A

4. Quick Check:

   map + copy() = new list with changed ages [OK]

Hint: Use map with copy() to update properties in list [OK]

Common Mistakes:

• Using forEach which returns Unit, not a list
• Trying to copy the whole list directly
• Ignoring destructuring or copy() usage