scala-trait-and-class-design

name	scala-trait-and-class-design
description	How to structure abstract base classes, trait hierarchies, and inheritance patterns in Scala for the tokenizer domain.

Trait vs Class Design

When to Use Traits

• Define contracts/interfaces: BaseTokenizer should likely be a trait
• Mix multiple behaviors: traits allow multiple inheritance of type and behavior
• Create sealed trait hierarchies: sealed trait TokenType

When to Use Classes

• When you need constructor parameters that aren't part of the type contract
• When you need mutable state (rare in Scala, but sometimes necessary)
• For concrete implementations that extend traits

Proper Abstraction for Tokenizer Hierarchy

Base Abstraction

trait BaseTokenizer {
  def tokenize(input: String): List[Token]
  // Other abstract methods
}

Concrete Implementations

class StringTokenizer extends BaseTokenizer {
  override def tokenize(input: String): List[Token] = {
    // implementation
  }
}

Factory/Builder Pattern

• Use companion object's apply method for construction
• Use builder for complex configuration
• Avoid passing too many parameters to constructors

Extension Methods

• For adding utility functions, use Scala 3 extension methods or implicit classes (Scala 2.13)
• Example: add methods to existing classes without inheritance