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Top 100 Scala Interview Questions and Answers

Top 100 Scala Interview Questions and Answers
Contents show

1. What is Scala?

Answer:
Scala is a general-purpose programming language that combines functional programming with object-oriented programming. It runs on the Java Virtual Machine (JVM) and is compatible with existing Java code. Scala is concise, expressive, and emphasizes immutability.

Official Reference: Scala Official Website


2. Explain the concept of immutability in Scala.

Answer:
In Scala, immutability means that once an object is created, its state cannot be changed. This leads to safer and more predictable code. For example, val is used to declare immutable variables, and var is used for mutable ones.

Official Reference: Scala Immutability


3. What is a higher-order function in Scala?

Answer:
A higher-order function is a function that takes one or more functions as arguments or returns a function as a result. This is a fundamental concept in functional programming and is well-supported in Scala.

Official Reference: Higher-Order Functions in Scala


4. Provide an example of a higher-order function in Scala.

Answer:

def applyTwice(f: Int => Int, x: Int): Int = f(f(x))
val addOne: Int => Int = _ + 1
val result = applyTwice(addOne, 1) // Result will be 3

In this example, applyTwice takes a function f and an integer x, and applies f twice to x.

Official Reference: Higher-Order Functions in Scala


5. What is pattern matching in Scala?

Answer:
Pattern matching is a powerful feature in Scala that allows you to match data against patterns and execute code based on the match. It’s similar to a switch statement in other languages but much more versatile.

Official Reference: Pattern Matching in Scala


6. Provide an example of pattern matching in Scala.

Answer:

def matchTest(x: Int): String = x match {
  case 1 => "One"
  case 2 => "Two"
  case _ => "Many"
}

val result = matchTest(3) // Result will be "Many"

In this example, matchTest takes an integer x and matches it against different cases.

Official Reference: Pattern Matching in Scala


7. What is a case class in Scala?

Answer:
A case class in Scala is a special type of class that is optimized for immutable data modeling. It automatically provides methods like toString, equals, hashCode, and a companion object with an apply method for easy instance creation.

Official Reference: Scala Case Classes


8. Provide an example of a case class in Scala.

Answer:

case class Person(name: String, age: Int)

val john = Person("John Doe", 30)
val jane = Person("Jane Doe", 28)

println(john.name) // Output: "John Doe"

In this example, Person is a case class with name and age fields. Instances can be created without using the new keyword.

Official Reference: Scala Case Classes


9. What is an Option in Scala?

Answer:
Option is a container type in Scala that represents an optional value. It can either be Some(value) if a value is present, or None if it’s absent. Option is commonly used to handle potentially missing values, reducing null pointer exceptions.

Official Reference: Scala Option


10. Provide an example of using Option in Scala.

Answer:

val maybeValue: Option[Int] = Some(42)
val missingValue: Option[Int] = None

val result = maybeValue.getOrElse(0) // Result will be 42
val defaultResult = missingValue.getOrElse(0) // Result will be 0

In this example, maybeValue contains a value, while missingValue is None. The getOrElse method provides a default value if the value is missing.

Official Reference: Scala Option


11. What is an Either type in Scala?

Answer:
Either is a type in Scala that represents a value of one of two possible types: Left or Right. It’s often used to represent the result of computations that may fail.

Official Reference: Scala Either


12. Provide an example of using Either in Scala.

Answer:

def divide(x: Int, y: Int): Either[String, Int] =
  if (y == 0) Left("Division by zero")
  else Right(x / y)

val result = divide(6, 2) // Result will be Right(3)
val errorResult = divide(6, 0) // Result will be Left("Division by zero")

In this example, divide returns an Either containing either an error message or a result.

Official Reference: Scala Either


13. What is a higher-order function in Scala?

Answer:
A higher-order function is a function that takes one or more functions as arguments or returns a function as a result. This is a fundamental concept in functional programming and is well-supported in Scala.

Official Reference: Higher-Order Functions in Scala


14. Provide an example of a higher-order function in Scala.

Answer:

def applyTwice(f: Int => Int, x: Int): Int = f(f(x))
val addOne: Int => Int = _ + 1
val result = applyTwice(addOne, 1) // Result will be 3

In this example, applyTwice takes a function f and an integer x, and applies f twice to x.

Official Reference: Higher-Order Functions in Scala


15. What is partial function application in Scala?

Answer:
Partial function application is a technique where you fix some of the parameters of a function to create a new function with fewer parameters. In Scala, you can achieve this using underscores (_).

Official Reference: Partial Function Application in Scala


16. Provide an example of partial function application in Scala.

Answer:

def add(x: Int, y: Int) = x + y
val add2 = add(2, _: Int) // Creates a new function with y fixed to 2

val result = add2(3) // Result will be 5

In this example, add2 is a new function created by fixing y to 2.

Official Reference: Partial Function Application in Scala


17. What is tail recursion in Scala?

Answer:
Tail recursion is a special type of recursion where the recursive call is the last operation performed in the function. This allows the Scala compiler to optimize the recursion into a loop, avoiding stack overflow errors.

Official Reference: Tail Recursion in Scala


18. Provide an example of a tail-recursive function in Scala.

Answer:

def factorial(n: Int): Int = {
  @annotation.tailrec
  def factorialHelper(x: Int, accumulator: Int): Int =
    if (x == 1) accumulator
    else factorialHelper(x - 1, accumulator * x)

  factorialHelper(n, 1)
}

val result = factorial(5) // Result will be 120

In this example, factorial is a tail-recursive function that calculates the factorial of a number.

Official Reference: Tail Recursion in Scala


19. What is a singleton object in Scala?

Answer:
A singleton object in Scala is an object that is defined using the object keyword instead of class. It is similar to a class but can only have one instance. Singleton objects are used to hold utility methods, define entry points, and manage shared resources.

Official Reference: Singleton Objects in Scala


20. Provide an example of a singleton object in Scala.

Answer:

object Logger {
  def log(message: String): Unit = println(s"Log: $message")
}

Logger.log("Hello, World!") // Output: "Log: Hello, World!"

In this example, Logger is a singleton object with a log method.

Official Reference: Singleton Objects in Scala


21. What is a trait in Scala?

Answer:
A trait in Scala is similar to an interface in Java, but it can also contain concrete methods. Traits are used to define a set of abstract and concrete members that can be mixed into classes. A class can extend multiple traits.

Official Reference: Scala Traits


22. Provide an example of using a trait in Scala.

Answer:

trait Greeter {
  def greet(): Unit = println("Hello!")
}

class Person extends Greeter {
  def introduce(): Unit = println("I am a person.")
}

val john = new Person()
john.greet() // Output: "Hello!"
john.introduce() // Output: "I am a person."

In this example, Greeter is a trait that is mixed into the Person class.

Official Reference: Scala Traits


23. What is a case object in Scala?

Answer:
A case object is similar to a case class but without any constructor parameters. It’s often used to represent singleton values or messages in an application.

Official Reference: Scala Case Objects


24. Provide an example of a case object in Scala.

Answer:

case object EmptyList

def processList(list: List[Int]): String = list match {
  case EmptyList => "List is empty"
  case _ => "List is not empty"
}

val myList = List(1, 2, 3)
val result = processList(myList) // Result will be "List is not empty"

In this example, EmptyList is a case object used to represent an empty list.

Official Reference: Scala Case Objects


25. What is pattern matching in Scala?

Answer:
Pattern matching is a powerful feature in Scala that allows you to match data against patterns and execute code based on the match. It’s similar to a switch statement in other languages but much more versatile.

Official Reference: Pattern Matching in Scala


26. Provide an example of pattern matching in Scala.

Answer:

def matchTest(x: Int): String = x match {
  case 1 => "One"
  case 2 => "Two"
  case _ => "Many"
}

val result = matchTest(3) // Result will be "Many"

In this example, matchTest takes an integer x and matches it against different cases.

Official Reference: Pattern Matching in Scala


27. What is the for comprehension in Scala?

Answer:
A for comprehension in Scala is used to work with monadic types like collections, Option, and Either. It provides a concise way to perform operations on elements within these types using a familiar syntax.

Official Reference: Scala for Comprehensions


28. Provide an example of using a for comprehension in Scala.

Answer:

val numbers = List(1, 2, 3, 4, 5)
val result = for {
  n <- numbers
  if n % 2 == 0
} yield n * 2

// Result will be List(4, 8)

In this example, the for comprehension doubles even numbers in a list.

Official Reference: Scala for Comprehensions


29. What is an implicit parameter in Scala?

Answer:
Implicit parameters are values that are passed implicitly to a method or function. They are often used for dependency injection and to provide context without explicitly passing parameters.

Official Reference: Implicit Parameters in Scala


30. Provide an example of using an implicit parameter in Scala.

Answer:

case class User(id: Int)

def greetUser(user: User)(implicit greeting: String): String =
  s"$greeting, User#${user.id}"

implicit val defaultGreeting: String = "Hello"

val user = User(1)
val greetingMessage = greetUser(user) // Result will be "Hello, User#1"

In this example, the greetUser function takes an implicit greeting parameter.

Official Reference: Implicit Parameters in Scala


31. What is a higher-kinded type in Scala?

Answer:
A higher-kinded type is a type that takes a type constructor as a parameter. It allows the creation of generic data structures that can operate on different types of type constructors, like lists, options, and more.

Official Reference: Higher-Kinded Types in Scala


32. Provide an example of a higher-kinded type in Scala.

Answer:

trait Functor[F[_]] {
  def map[A, B](fa: F[A])(f: A => B): F[B]
}

implicit val optionFunctor: Functor[Option] = new Functor[Option] {
  def map[A, B](fa: Option[A])(f: A => B): Option[B] = fa.map(f)
}

val result = optionFunctor.map(Some(42))(_ * 2) // Result will be Some(84)

In this example, Functor is a higher-kinded type that defines a map method for different type constructors, like Option.

Official Reference: Higher-Kinded Types in Scala


33. What is type erasure in Scala?

Answer:
Type erasure is a feature of the Scala compiler that erases generic type information at runtime. This means that generic types are not available at runtime, which can lead to limitations in pattern matching and other operations.

Official Reference: Type Erasure in Scala


34. Provide an example of type erasure in Scala.

Answer:

def isListInt(x: Any): Boolean = x match {
  case _: List[Int] => true
  case _ => false
}

val result = isListInt(List(1, 2, 3)) // Result will be true

In this example, isListInt tries to match if the input is a List of Int, but due to type erasure, it matches any List.

Official Reference: Type Erasure in Scala


35. What is the Future type in Scala?

Answer:
Future is a type in Scala used for asynchronous programming. It represents a value that may not be available yet. It’s commonly used for concurrent programming and non-blocking I/O operations.

Official Reference: Scala Futures


36. Provide an example of using Future in Scala.

Answer:

import scala.concurrent.Future
import scala.concurrent.ExecutionContext.Implicits.global

val futureResult: Future[Int] = Future {
  Thread.sleep(1000)
  42
}

futureResult.onComplete {
  case Success(value) => println(s"Result: $value")
  case Failure(exception) => println(s"Error: $exception")
}

In this example, a Future is created to perform a computation asynchronously.

Official Reference: Scala Futures


37. What is a type class in Scala?

Answer:
A type class in Scala is a design pattern that allows you to extend the behavior of existing types without modifying them. It provides a way to define a set of operations that can be applied to a type, enabling ad-hoc polymorphism.

Official Reference: Scala Type Classes


38. Provide an example of using a type class in Scala.

Answer:

trait Printable[A] {
  def print(value: A): String
}

object PrintableInstances {
  implicit val printableString: Printable[String] = (value: String) => value
  implicit val printableInt: Printable[Int] = (value: Int) => value.toString
}

object PrintableSyntax {
  implicit class PrintableOps[A](value: A) {
    def print(implicit printable: Printable[A]): String = printable.print(value)
  }
}

import PrintableInstances._
import PrintableSyntax._

val str = "Hello, World!"
val num = 42

val strPrinted = str.print // Result will be "Hello, World!"
val numPrinted = num.print // Result will be "42"

In this example, we define a type class Printable and provide instances for String and Int. We then use implicit classes to enrich existing types with the print method.

Official Reference: Scala Type Classes


39. What is a higher-order kind in Scala?

Answer:
A higher-order kind is a kind that abstracts over other kinds. In Scala, it allows you to define type constructors that can operate on other type constructors.

Official Reference: Higher-Kinded Types and Kinds in Scala


40. Provide an example of a higher-order kind in Scala.

Answer:

trait Functor[F[_]] {
  def map[A, B](fa: F[A])(f: A => B): F[B]
}

implicit val listFunctor: Functor[List] = new Functor[List] {
  def map[A, B](fa: List[A])(f: A => B): List[B] = fa.map(f)
}

val numbers = List(1, 2, 3)
val result = Functor[List].map(numbers)(_ * 2) // Result will be List(2, 4, 6)

In this example, Functor is a higher-order kind that abstracts over type constructors like List.

Official Reference: Higher-Kinded Types and Kinds in Scala


41. What is covariance and contravariance in Scala?

Answer:
Covariance and contravariance are concepts related to type hierarchies.

  • Covariance: It allows you to use a more derived type (subclass) than originally specified. For example, if A is a subclass of B, then List[A] is considered a subclass of List[B].
  • Contravariance: It allows you to use a more generic type (superclass) than originally specified. For example, if A is a subclass of B, then Function1[B, _] is considered a subclass of Function1[A, _].

Official Reference: Covariance and Contravariance in Scala


42. Provide an example of covariance in Scala.

Answer:

class Animal
class Dog extends Animal

val dogs: List[Dog] = List(new Dog, new Dog)
val animals: List[Animal] = dogs // Covariance allows this assignment

In this example, List[Dog] is considered a subclass of List[Animal] due to covariance.

Official Reference: Covariance and Contravariance in Scala


43. Provide an example of contravariance in Scala.

Answer:

class Animal
class Dog extends Animal

class Printer[-A] {
  def print(value: A): Unit = println(value)
}

val animalPrinter: Printer[Animal] = new Printer[Dog] // Contravariance allows this assignment
animalPrinter.print(new Animal) // Prints "Animal"

In this example, Printer[Animal] is considered a subclass of Printer[Dog] due to contravariance.

Official Reference: Covariance and Contravariance in Scala


44. What is type projection in Scala?

Answer:
Type projection in Scala allows you to refer to the type of a member of a class or trait without specifying the specific instance. It’s denoted as # followed by the member’s name.

Official Reference: Type Projections in Scala


45. Provide an example of type projection in Scala.

Answer:

class Container {
  type Item = String
  val item: Item = "Hello, World!"
}

def printItem(container: Container): Unit = {
  val item: container.Item = container.item
  println(item)
}

val box = new Container
printItem(box) // Prints "Hello, World!"

In this example, container.Item refers to the type String defined in Container.

Official Reference: Type Projections in Scala


46. What are implicits in Scala?

Answer:
Implicits in Scala are a powerful feature that allows the compiler to automatically insert code to satisfy a given requirement. They are used for a variety of purposes, including type conversions, providing default values, and more.

Official Reference: Implicit Parameters and Conversions in Scala


47. Provide an example of using implicits in Scala.

Answer:

case class Person(name: String)

def greet(person: Person): String = s"Hello, ${person.name}!"

implicit val defaultPerson = Person("John Doe")

val greeting = greet // The compiler inserts defaultPerson as an implicit argument

In this example, the greet function expects a Person argument, but the compiler automatically inserts defaultPerson due to the implicit modifier.

Official Reference: Implicit Parameters and Conversions in Scala


48. What is a context bound in Scala?

Answer:
A context bound is a syntactic sugar that simplifies the usage of type classes. It is denoted by [T: TypeClass], which means there is an implicit parameter of type TypeClass[T] available.

Official Reference: Context Bounds in Scala


49. Provide an example of using a context bound in Scala.

Answer:

trait Show[T] {
  def show(value: T): String
}

def printWithShow[T: Show](value: T): Unit = {
  val showInstance = implicitly[Show[T]]
  println(showInstance.show(value))
}

implicit val intShow: Show[Int] = (value: Int) => s"Int($value)"

printWithShow(42) // Prints "Int(42)"

In this example, the printWithShow function has a context bound of Show, meaning it requires an implicit instance of Show[T].

Official Reference: Context Bounds in Scala


50. What is a view bound in Scala?

Answer:
A view bound is a syntactic sugar similar to a context bound, but it allows implicit conversions from one type to another.

Official Reference: View Bounds in Scala


51. Provide an example of using a view bound in Scala.

Answer:

case class Money(value: Double)

trait ToDouble[T] {
  def toDouble(value: T): Double
}

def calculateTotal[T <% ToDouble](items: List[T]): Double = {
  items.map(_.toDouble).sum
}

implicit val moneyToDouble = new ToDouble[Money] {
  def toDouble(value: Money): Double = value.value
}

val total = calculateTotal(List(Money(10.5), Money(20.0))) // Result will be 30.5

In this example, the calculateTotal function uses a view bound to convert items to Double before summing them.

Official Reference: View Bounds in Scala


52. What is a self-type annotation in Scala?

Answer:
A self-type annotation in Scala is a way to declare that a trait must be mixed into another trait or class. It enforces that the required dependencies are present.

Official Reference: Self-type Annotations in Scala


53. Provide an example of using a self-type annotation in Scala.

Answer:

trait Logger {
  def log(message: String): Unit
}

trait Service {
  self: Logger => // This enforces that any class mixing in Service must also mix in Logger
  def performAction(): Unit = {
    log("Performing action...")
  }
}

class MyService extends Service with Logger {
  def log(message: String): Unit = println(message)
}

val service = new MyService
service.performAction() // Output: "Performing action..."

In this example, Service requires a Logger to be mixed in, enforced by the self-type annotation.

Official Reference: Self-type Annotations in Scala


54. What is a cake pattern in Scala?

Answer:
The cake pattern is a way to achieve dependency injection in Scala without using any DI frameworks. It leverages self-type annotations to wire dependencies together.

Official Reference: The Cake Pattern in Scala


55. Provide an example of using the cake pattern in Scala.

Answer:

trait UserServiceComponent {
  def userService: UserService

  trait UserService {
    def getUser(id: Int): String
  }
}

trait UserRepositoryComponent {
  def userRepository: UserRepository

  trait UserRepository {
    def findUserById(id: Int): String
  }
}

trait ProductionEnvironment extends UserServiceComponent with UserRepositoryComponent {
  val userRepository = new UserRepository {
    def findUserById(id: Int): String = s"User with ID $id"
  }

  val userService = new UserService {
    def getUser(id: Int): String = userRepository.findUserById(id)
  }
}

object Application extends ProductionEnvironment {
  def main(args: Array[String]): Unit = {
    val user = userService.getUser(42)
    println(user) // Output: "User with ID 42"
  }
}

In this example, we define traits for UserServiceComponent and UserRepositoryComponent and implement them using the ProductionEnvironment. This allows for easy swapping of components.

Official Reference: The Cake Pattern in Scala


56. What is a higher-order function in Scala?

Answer:
A higher-order function in Scala is a function that either takes one or more functions as arguments or returns a function as its result. This allows for functions to be treated as first-class citizens.

Official Reference: Higher-Order Functions in Scala


57. Provide an example of a higher-order function in Scala.

Answer:

def mathOperation(x: Int, y: Int, operation: (Int, Int) => Int): Int = {
  operation(x, y)
}

val addition = (a: Int, b: Int) => a + b
val subtraction = (a: Int, b: Int) => a - b

val resultAddition = mathOperation(10, 5, addition) // Result will be 15
val resultSubtraction = mathOperation(10, 5, subtraction) // Result will be 5

In this example, mathOperation is a higher-order function that takes an operation function as an argument.

Official Reference: Higher-Order Functions in Scala


58. What is a curried function in Scala?

Answer:
A curried function in Scala is a function that takes multiple arguments and transforms it into a sequence of functions, each taking a single argument.

Official Reference: Currying in Scala


59. Provide an example of a curried function in Scala.

Answer:

def add(x: Int)(y: Int): Int = x + y

val addFive = add(5) _ // Partially applied function

val result = addFive(3) // Result will be 8

In this example, add is a curried function that takes x and returns a function that takes y.

Official Reference: Currying in Scala


60. What is pattern matching in Scala?

Answer:
Pattern matching in Scala is a powerful feature for checking a value against a pattern. It can be used to match values, types, and even structures.

Official Reference: Pattern Matching in Scala


61. Provide an example of pattern matching in Scala.

Answer:

def matchTest(x: Int): String = x match {
  case 1 => "One"
  case 2 => "Two"
  case _ => "Other"
}

val result = matchTest(3) // Result will be "Other"

In this example, matchTest uses pattern matching to return a string based on the value of x.

Official Reference: Pattern Matching in Scala


62. What is a case class in Scala?

Answer:
A case class in Scala is a special class that is optimized for immutable data modeling. It provides a concise way to define data with a default implementation of methods like toString, equals, hashCode, and more.

Official Reference: Case Classes in Scala


63. Provide an example of a case class in Scala.

Answer:

case class Person(name: String, age: Int)

val john = Person("John Doe", 30)

val name = john.name // Accessing the name property

In this example, Person is a case class with properties name and age. It can be instantiated without the new keyword.

Official Reference: Case Classes in Scala


64. What is an option in Scala?

Answer:
Option is a container type in Scala that may or may not contain a value. It helps handle cases where a value may be absent, reducing the need for null checks.

Official Reference: Options in Scala


65. Provide an example of using Option in Scala.

Answer:

val maybeName: Option[String] = Some("John")

val length = maybeName match {
  case Some(name) => name.length
  case None => 0
}

In this example, maybeName is an Option that contains a Some with a name. Pattern matching is used to handle both cases.

Official Reference: Options in Scala


66. What is the difference between map and flatMap in Scala?

Answer:
map is used to apply a function to the contents of an Option if it is not None. flatMap is used when the applied function also returns an Option.

Official Reference: map and flatMap in Scala


67. Provide an example of using map and flatMap in Scala.

Answer:

val maybeNumber: Option[Int] = Some(5)

val mappedResult = maybeNumber.map(num => num * 2) // Result will be Some(10)
val flatMappedResult = maybeNumber.flatMap(num => Some(num * 2)) // Result will be Some(10)

In this example, map and flatMap are used to double the value inside the Option.

Official Reference: map and flatMap in Scala


68. What is a for-comprehension in Scala?

Answer:
A for-comprehension in Scala is a way to iterate over collections or sequences in a concise and expressive manner. It combines loops, filters, and assignments into a single construct.

Official Reference: For-Comprehensions in Scala


69. Provide an example of using a for-comprehension in Scala.

Answer:

val numbers = Seq(1, 2, 3, 4, 5)

val doubledEvenNumbers = for {
  num <- numbers
  if num % 2 == 0
} yield num * 2

In this example, the for-comprehension filters even numbers and doubles them.

Official Reference: For-Comprehensions in Scala


70. What is an actor in Scala?

Answer:
An actor in Scala is a concurrency model for managing state and processing messages. It provides a lightweight and efficient way to handle concurrent operations.

Official Reference: Actors in Scala


71. Provide an example of using actors in Scala.

Answer:

import akka.actor.{Actor, ActorSystem, Props}

case class Greet(name: String)

class Greeter extends Actor {
  def receive = {
    case Greet(name) => println(s"Hello, $name!")
  }
}

val system = ActorSystem("GreeterSystem")
val greeter = system.actorOf(Props[Greeter], "greeter")

greeter ! Greet("John") // Output: "Hello, John!"

In this example, an actor Greeter is defined to handle the message Greet.

Official Reference: Actors in Scala


72. What is pattern matching in Akka?

Answer:
Pattern matching in Akka is a way to define behavior for actors based on the messages they receive. It allows for selective handling of different message types.

Official Reference: Pattern Matching in Akka


73. Provide an example of using pattern matching in Akka.

Answer:

import akka.actor.{Actor, ActorSystem, Props}

case class Greet(name: String)
case class ThankYou(name: String)

class Greeter extends Actor {
  def receive = {
    case Greet(name) => println(s"Hello, $name!")
    case ThankYou(name) => println(s"You're welcome, $name!")
  }
}

val system = ActorSystem("GreeterSystem")
val greeter = system.actorOf(Props[Greeter], "greeter")

greeter ! Greet("John") // Output: "Hello, John!"
greeter ! ThankYou("Jane") // Output: "You're welcome, Jane!"

In this example, the Greeter actor uses pattern matching to handle both Greet and ThankYou messages.

Official Reference: Pattern Matching in Akka


74. What is tail recursion in Scala?

Answer:
Tail recursion is a special type of recursion where the recursive call is the last operation performed in a function. It can be optimized by the compiler to avoid stack overflow errors.

Official Reference: Tail Recursion in Scala


75. Provide an example of a tail-recursive function in Scala.

Answer:

def factorial(n: Int): Int = {
  def factorialHelper(n: Int, acc: Int): Int = {
    if (n == 0) acc
    else factorialHelper(n - 1, acc * n)
  }

  factorialHelper(n, 1)
}

In this example, factorial is a tail-recursive function that calculates the factorial of a number.

Official Reference: Tail Recursion in Scala


76. What is a partial function in Scala?

Answer:
A partial function in Scala is a function that is defined for a subset of its input domain. It is only defined for certain input values and may throw an exception for others.

Official Reference: Partial Functions in Scala


77. Provide an example of a partial function in Scala.

Answer:

val divide: PartialFunction[Int, Int] = {
  case d: Int if d != 0 => 42 / d
}

val result = divide(7) // Result will be 6

In this example, divide is a partial function that is only defined for non-zero integers.

Official Reference: Partial Functions in Scala


78. What is lazy evaluation in Scala?

Answer:
Lazy evaluation in Scala is a technique where the evaluation of a value is deferred until it is actually needed. This can improve performance and reduce unnecessary computations.

Official Reference: Lazy Evaluation in Scala


79. Provide an example of lazy evaluation in Scala.

Answer:

lazy val expensiveOperation: Int = {
  println("Performing expensive operation")
  42
}

val result = expensiveOperation // "Performing expensive operation" will be printed

In this example, expensiveOperation is only evaluated when it is actually accessed.

Official Reference: Lazy Evaluation in Scala


80. What is a higher-order function in Scala?

Answer:
A higher-order function in Scala is a function that either takes one or more functions as arguments or returns a function as a result. It allows for the composition and abstraction of behavior.

Official Reference: Higher-Order Functions in Scala


81. Provide an example of a higher-order function in Scala.

Answer:

def applyTwice(f: Int => Int, x: Int): Int = f(f(x))

val result = applyTwice(_ + 1, 2) // Result will be 4

In this example, applyTwice is a higher-order function that takes a function f and applies it twice to x.

Official Reference: Higher-Order Functions in Scala


82. What is a monad in Scala?

Answer:
A monad in Scala is a design pattern that provides a way to sequence computations or operations in a functional programming style. It is used for handling side effects, asynchronous operations, and more.

Official Reference: Monads in Scala


83. Provide an example of using a monad in Scala.

Answer:

val optionValue: Option[Int] = Some(42)
val result = optionValue.flatMap(x => Some(x * 2)) // Result will be Some(84)

In this example, flatMap is used on an Option monad to perform a computation on the value inside.

Official Reference: Monads in Scala


84. What is immutability in Scala?

Answer:
Immutability in Scala refers to the property of objects or variables whose state cannot be modified after they are created. It promotes safer and more predictable code.

Official Reference: Immutability in Scala


85. Provide an example of an immutable data structure in Scala.

Answer:

val list = List(1, 2, 3, 4, 5)
val modifiedList = list.map(_ * 2) // Result will be List(2, 4, 6, 8, 10)

In this example, list is an immutable List where map creates a new list without modifying the original.

Official Reference: Immutability in Scala


86. What is a case class in Scala?

Answer:
A case class in Scala is a class that is optimized for immutable data modeling. It automatically provides methods for equality, pattern matching, and more.

Official Reference: Case Classes in Scala


87. Provide an example of a case class in Scala.

Answer:

case class Person(name: String, age: Int)

val john = Person("John Doe", 30)
val jane = Person("Jane Doe", 25)

val isSamePerson = john == jane // Result will be false

In this example, Person is a case class with fields name and age.

Official Reference: Case Classes in Scala


88. What is pattern matching in Scala?

Answer:
Pattern matching in Scala is a powerful mechanism for checking a value against a pattern. It allows for conditional execution based on the structure of the data.

Official Reference: Pattern Matching in Scala


89. Provide an example of using pattern matching in Scala.

Answer:

val dayOfWeek: Int = 3

val dayName = dayOfWeek match {
  case 1 => "Sunday"
  case 2 => "Monday"
  case 3 => "Tuesday"
  case _ => "Unknown"
}

In this example, dayName will be “Tuesday” because dayOfWeek is matched to the pattern 3.

Official Reference: Pattern Matching in Scala


90. What is a companion object in Scala?

Answer:
A companion object in Scala is an object with the same name as a class. It is used to contain static methods or values that are related to the class.

Official Reference: Companion Objects in Scala


91. Provide an example of a companion object in Scala.

Answer:

class Circle(val radius: Double)

object Circle {
  def apply(radius: Double): Circle = new Circle(radius)
}

val circle = Circle(5.0)

In this example, the companion object Circle provides an apply method for creating instances of the Circle class.

Official Reference: Companion Objects in Scala


92. What is a trait in Scala?

Answer:
A trait in Scala is a special kind of class that is used to extend the abilities of a class. It allows for the mixing of multiple traits to achieve multiple inheritance-like behavior.

Official Reference: Traits in Scala


93. Provide an example of a trait in Scala.

Answer:

trait Shape {
  def area(): Double
}

class Circle(radius: Double) extends Shape {
  def area(): Double = Math.PI * radius * radius
}

In this example, Shape is a trait that defines a method area. The Circle class extends the Shape trait.

Official Reference: Traits in Scala


94. What is a future in Scala?

Answer:
A future in Scala is a placeholder for a value that may not be available yet. It represents a computation that may be performed asynchronously.

Official Reference: Futures in Scala


95. Provide an example of using a future in Scala.

Answer:

import scala.concurrent.Future
import scala.concurrent.ExecutionContext.Implicits.global

val futureResult: Future[Int] = Future {
  Thread.sleep(1000)
  42
}

futureResult.onComplete {
  case Success(result) => println(s"The result is $result")
  case Failure(exception) => println(s"An error occurred: $exception")
}

In this example, futureResult represents a future computation that returns the value 42 after a delay.

Official Reference: Futures in Scala


96. What is a partial function in Scala?

Answer:
A partial function in Scala is a function that is only defined for certain input values and may throw an exception for others.

Official Reference: Partial Functions in Scala


97. Provide an example of a partial function in Scala.

Answer:

val divide: PartialFunction[Int, Int] = {
  case d: Int if d != 0 => 42 / d
}

val result = divide(7) // Result will be 6

In this example, divide is a partial function that is only defined for non-zero integers.

Official Reference: Partial Functions in Scala


98. What is a higher-order function in Scala?

Answer:
A higher-order function in Scala is a function that can take other functions as arguments or return them as results. It enables functional programming paradigms.

Official Reference: Higher-Order Functions in Scala


99. Provide an example of a higher-order function in Scala.

Answer:

def applyTwice(f: Int => Int, x: Int): Int = f(f(x))

val addOne: Int => Int = _ + 1
val result = applyTwice(addOne, 2) // Result will be 4

In this example, applyTwice is a higher-order function that takes a function f and an integer x, then applies f twice to x.

Official Reference: Higher-Order Functions in Scala


100. What is currying in Scala?

Answer:
Currying in Scala is the technique of transforming a function with multiple arguments into a series of functions with a single argument. It enables partial application.

Official Reference: Currying in Scala