E112: Unable to Extend Sealed Class

This error is emitted when attempting to extend a sealed class or trait from a different source file.

Sealed classes and traits can only be extended in the same source file where they are declared. This restriction enables exhaustive pattern matching.

Example

scala

sealed trait Animal
case class Dog(name: String) extends Animal

scala

case class Cat(name: String) extends Animal

Error

scala

-- [E112] Syntax Error: example.scala:1:32
1 |case class Cat(name: String) extends Animal
  |                                     ^^^^^^
  |                     Cannot extend sealed trait Animal in a different source file

Solution

scala

// Define all subclasses in the same file as the sealed trait
sealed trait Animal
case class Dog(name: String) extends Animal
case class Cat(name: String) extends Animal

scala

// Or use an open or abstract class instead of sealed
abstract class Animal
case class Dog(name: String) extends Animal
// Cat can now be defined in another file

<aside class="warning"> This reference page was created with LLM assistance - the description of the error code may not be accurate or cover all possible scenarios. </aside>