Scala Implicits and Type Classes

Question 1

Which keyword is used to define an implicit value in Scala 2?

Accepted Answer

implicit

Answer

In Scala 2, the `implicit` keyword marks a value, method, or class so the compiler can supply it automatically when required.

Question 2

In Scala 3, which keyword replaces `implicit val` for defining implicit instances?

Accepted Answer

given

Answer

Scala 3 introduces `given` as a cleaner replacement for `implicit val`, making the intent of providing a type class instance explicit.

Question 3

What best describes a type class in Scala?

Accepted Answer

A pattern using traits and implicits to achieve ad-hoc polymorphism

Answer

A type class is a trait parameterized by a type, with implicit instances providing implementations, enabling polymorphism without inheritance.

Question 4

Which of the following correctly declares an implicit parameter in Scala 2?

Accepted Answer

def foo(implicit x: Int): Unit

Answer

In Scala 2, `implicit` is placed at the start of a parameter list to mark all parameters in that list as implicit.

Question 5

What happens when the Scala compiler cannot find a required implicit value in scope?

Accepted Answer

It produces a compile-time error

Answer

Missing implicits are caught at compile time; the compiler reports an error stating it could not find an implicit value for the required type.

Scala Practice Test