Scala Implicits and Type Classes 2

Question 1

What is the primary use of an implicit class in Scala 2?

Accepted Answer

To add extension methods to an existing type

Answer

To create classes that are automatically instantiated at startup

Answer

To define classes whose constructor arguments are implicit

Answer

To create singleton companion objects automatically

Question 2

In Scala 3, which keyword marks a parameter as one that should be filled by a `given` instance?

Accepted Answer

using

Answer

implicit

Answer

given

Answer

infer

Question 3

Which syntax correctly defines a `Show[Int]` type class instance in Scala 2?

Accepted Answer

implicit val intShow: Show[Int] = new Show[Int] { def show(n: Int): String = n.toString }

Answer

given intShow: Show[Int] = new Show[Int] { def show(n: Int): String = n.toString }

Answer

type Show[Int] = new Show[Int] { def show(n: Int): String = n.toString }

Answer

val implicit intShow: Show[Int] = new Show[Int] { def show(n: Int): String = n.toString }

Question 4

What does the `@implicitNotFound` annotation do in Scala?

Accepted Answer

Provides a custom, user-friendly error message when an implicit for that type cannot be found

Answer

Prevents any implicit from being resolved for the annotated type

Answer

Marks a class as excluded from implicit search

Answer

Disables implicit conversions for a specific type parameter

Question 5

In Scala 2, in what priority order does the compiler search for implicit values?

Accepted Answer

Local scope first, then imports, then companion objects of involved types

Answer

Companion objects first, then local scope, then imports

Answer

Imports first, then local scope, then companion objects

Answer

Global scope only, regardless of local definitions

Question 6

What does the context bound syntax `def foo[T: Ordering](x: T, y: T)` mean in Scala?

Accepted Answer

The method requires an implicit `Ordering[T]` parameter, supplied automatically by the compiler

Answer

T must be a subtype of Ordering

Answer

T is bounded to only ordered primitive types

Answer

The method returns an Ordering instance for T

Question 7

Which Scala feature allows you to retroactively add type class instances to types you don't own or control?

Accepted Answer

Implicit (or given) instances defined outside the type

Answer

Inheritance and subclassing

Answer

Mixin composition with traits

Answer

Type aliases and newtypes