Scala Pattern Matching and Case Classes 2

Question 1

What is a sealed trait in Scala and why is it useful with pattern matching?

Accepted Answer

A trait whose subclasses are defined in the same file, enabling exhaustive matching

Answer

A sealed trait restricts all subclasses to the same file, allowing the compiler to warn about non-exhaustive match expressions.

Question 2

How do you match on a List's head and tail in Scala?

Accepted Answer

case h :: t =>

Answer

The cons operator `::` is used in patterns to destructure a List into its head element and its tail list.

Question 3

What happens if no pattern matches in a Scala match expression?

Accepted Answer

A MatchError is thrown at runtime

Answer

If no case matches in a Scala match expression, a `MatchError` is thrown at runtime, so always include a default case.

Question 4

Which Scala feature lets you add a condition to a pattern match case?

Accepted Answer

Pattern guard using `if`

Answer

A pattern guard adds an `if condition` after the pattern in a case clause, further restricting when that arm is selected.

Question 5

What does `copy` do on a Scala case class?

Accepted Answer

Returns a modified copy of the instance with specified fields changed

Answer

The auto-generated `copy` method creates a new case class instance with the same values, except for the fields you specify.

Scala Practice Test