Scala Traits and Type System

Question 1

What is a Scala trait?

Accepted Answer

An abstract type similar to a Java interface that can contain concrete implementations

Answer

A Scala trait is like a Java interface but can contain concrete method and field implementations, enabling mixin composition.

Question 2

How do you mix a trait into a class in Scala?

Accepted Answer

class Foo with Bar

Answer

Use the `with` keyword to mix additional traits into a class after the initial `extends` declaration.

Question 3

What is the diamond problem in OOP and how does Scala solve it?

Accepted Answer

Ambiguity from multiple inheritance; Scala uses linearization to determine method resolution order

Answer

Scala resolves the diamond problem through C3 linearization, establishing a deterministic method resolution order for mixed-in traits.

Question 4

What is a type alias in Scala?

Accepted Answer

A new name given to an existing type using `type`

Answer

The `type` keyword creates an alias for an existing type, improving code readability without creating a new type.

Question 5

What is variance in Scala generics?

Accepted Answer

How subtyping relationships of type parameters relate to subtyping of parameterized types

Answer

Variance annotations (`+A` for covariance, `-A` for contravariance) control how generic type relationships map to subtype relationships.

Scala Practice Test