Scala Implicits and Type Classes 3

Question 1

In Scala 3, what is `summon[T]` equivalent to in Scala 2?

Accepted Answer

implicitly[T]

Answer

`summon[T]` in Scala 3 retrieves a `given` instance of type T from scope, performing the same role as `implicitly[T]` in Scala 2.

Question 2

Which syntax correctly defines a Scala 3 extension method that adds `double` to `Int`?

Accepted Answer

extension (n: Int) def double: Int = n * 2

Answer

Scala 3 introduces the `extension` keyword as first-class syntax for adding methods to existing types, replacing the implicit class workaround.

Question 3

What is 'implicit ambiguity' in Scala?

Accepted Answer

When two or more equally valid implicits exist in scope for the same type, causing a compile error

Answer

If the compiler finds multiple implicits of the same type in scope with equal priority, it cannot choose between them and reports an ambiguity error.

Question 4

What does the type constraint `implicit ev: A =:= B` assert in Scala?

Accepted Answer

That types A and B are exactly the same type

Answer

`=:=` is a type class provided by Scala's standard library whose instance exists only when A and B are the same type, enforcing type equality as a constraint.

Question 5

What is the Magnet pattern in Scala?

Accepted Answer

A design pattern using implicits to simulate method overloading on a single method

Answer

The Magnet pattern uses a sealed trait and implicit conversions to allow a single method to accept multiple argument types, avoiding JVM overloading limitations.

Scala Practice Test

Scala Practice Test

Scala Implicits and Type Classes 3