Scala Traits and Type System 2

Question 1

What is a type class in Scala?

Accepted Answer

A pattern using traits and implicits to add behavior to existing types without inheritance

Answer

Type classes are a pattern in Scala that uses traits and implicit parameters to define behavior for types outside their hierarchy.

Question 2

What is the `Nothing` type in Scala?

Accepted Answer

The type of exceptions; it is a subtype of every type

Answer

`Nothing` is at the bottom of the Scala type hierarchy and is a subtype of every type, used for expressions that never return.

Question 3

What does covariance (`+T`) mean for a Scala generic type?

Accepted Answer

If A extends B, then Container[A] extends Container[B]

Answer

A covariant type parameter `+T` means that if `A` is a subtype of `B`, then `Container[A]` is also a subtype of `Container[B]`.

Question 4

What is an implicit conversion in Scala?

Accepted Answer

An automatic type conversion triggered by the compiler when types don't match

Answer

Implicit conversions are functions marked `implicit` that the compiler calls automatically to convert one type to another when needed.

Question 5

Which Scala construct is used to define an abstract type member?

Accepted Answer

type T <: AnyRef inside a trait

Answer

Abstract type members are declared inside a trait or abstract class using `type T` with optional upper/lower bounds like `T <: AnyRef`.

Scala Practice Test