scala-213-type-hierarchy-and-modeling

name	scala-213-type-hierarchy-and-modeling
description	Define idiomatic Scala 2.13 type hierarchies and domain models, replacing Python's class structures and Enums with traits and case classes.

Sealed Traits and Case Objects for Enums

Scala 2.13 does not support the enum keyword. To represent a fixed set of types (like TokenType):

1. Define a sealed trait as the base type.
2. Define case object instances for each specific type. This ensures exhaustiveness checking during pattern matching.

Class Hierarchies

Replace Python base classes with a sealed trait or abstract class for the BaseTokenizer.

• Use a trait if you only define an interface.
• Use an abstract class if you need to provide common constructor parameters or shared logic for all tokenizers.

Data Representation

Use case class for the Token model. Case classes provide:

• Immutability by default.
• Built-in equals, hashCode, and toString.
• A .copy() method, which is essential for the withMetadata pattern.

The withMetadata Pattern

To implement withMetadata idiomatically, leverage the .copy() method of the Token case class. This allows you to return a new instance with updated fields without mutating the original object, maintaining functional purity.