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 final class with static methods

Answer

A type alias

Answer

A wrapper around a Java class

Question 2

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

Accepted Answer

class Foo with Bar

Answer

class Foo implements Bar

Answer

class Foo inherits Bar

Answer

class Foo extends Bar

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

A pattern for diamonds; solved by generics

Answer

A null pointer issue; solved with Option

Answer

A compilation error; solved with sealed traits

Question 4

What is a type alias in Scala?

Accepted Answer

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

Answer

A renamed import

Answer

An implicit conversion

Answer

A supertype declaration

Question 5

What is variance in Scala generics?

Accepted Answer

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

Answer

The variability of runtime performance

Answer

The mutability of generic collections

Answer

The version of the generic API

Question 6

What does `implicit` mean when applied to a parameter in Scala?

Accepted Answer

The compiler automatically finds and passes a matching value from implicit scope

Answer

The parameter is optional

Answer

The parameter is lazily evaluated

Answer

The parameter is inherited from a trait