🌟Scala 3 New Features

@Credit - Daniel Ciocîrlan, Kannupriya Kalra, Adrien Piquerez, Scala Center

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⚡ First Impressions: A Clear Roadmap

The course wasted no time. Instead of drowning me in theory, it broke Scala 3 into three digestible categories:

1. What’s Changed (Syntax, implicits, minor tweaks)

2. What’s Added (Enums, union types, match types)

3. What’s Removed (Deprecated syntax, abstract type projections)

No fluff—just a laser-focused guide to what actually matters in Scala 3.

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Scala 3 (Dotty) introduces groundbreaking features that enhance expressiveness, performance, and type safety. Having explored opaque types, traits with parameters, enums, and type lambdas, I’ve witnessed firsthand how these innovations simplify complex abstractions while maintaining zero-cost performance.

In this blog, I’ll break down these features with practical examples, comparing them to Scala 2 and highlighting why they matter for modern Scala development.

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1. Opaque Types: Zero-Cost Type Safety

The Problem in Scala 2

Previously, creating type-safe wrappers (e.g., UserId) required runtime overhead:

scala

case class UserId(value: String)  // Allocates extra memory

Scala 3’s Solution

Opaque types provide compile-time wrappers with no runtime cost:

scala

object UserDomain:
  opaque type UserId = String  // Internally a String, externally a unique type

  object UserId:
    def apply(value: String): UserId = value  // Factory method
    extension (id: UserId) def value: String = id  // Expose API

Key Benefits

✅ Zero runtime overhead (unlike case classes)
✅ Strict encapsulation (prevents accidental misuse)
✅ Domain-driven design (cleaner than type aliases)

Use Case: Ideal for high-performance systems (e.g., financial apps, large-scale data processing).

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2. Traits with Constructor Parameters

Scala 2 Limitation

Traits couldn’t take constructor arguments, forcing workarounds with abstract classes:

scala

trait Engine { def power: Int }  // Must be implemented by subclass

Scala 3’s Enhancement

Now, traits behave like abstract classes but retain mixin capabilities:

scala

trait Engine(power: Int)  // Constructor parameter
class Car extends Engine(300)  // Must pass argument

Caveats

⚠ Diamond inheritance requires uniform constructor args:

scala

trait A(x: Int); trait B extends A; trait C extends A
class D extends B with C(5)  // Compiler error (conflicting args)

Use Case: Modular configuration (e.g., dependency injection).

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3. First-Class Enums (No More Boilerplate!)

Scala 2’s Verbosity

Enums required manual ADTs:

scala

sealed trait Color  
case object Red extends Color  
case object Green extends Color  
// ...

Scala 3’s Elegance

Native enum syntax reduces boilerplate:

scala

enum Color:
  case Red, Green, Blue  // Auto-generates sealed hierarchy

Advanced Features:

• Parameterized enums (case RGB(r: Int, g: Int, b: Int))

• Methods & fields (def hexCode: String = ...)

• Companion objects (for factory methods)

Use Case: State machines, HTTP methods, and other fixed-value domains.

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4. Type Lambdas: Taming Higher-Kinded Types

The Problem in Scala 2

Partial type application (e.g., Either[String, *]) required kind-projector:

scala

// With kind-projector syntax  
Functor[Either[String, ?]]

Scala 3’s Native Solution

Type lambdas ([A] =>> F[A]) enable type-level functions:

scala

type EitherString[A] = [A] =>> Either[String, A]  // Partial application
given Monad[EitherString]  // Works with type classes

Why It Matters

🔹 Replaces kind-projector (no plugin needed)
🔹 Enables monad instances for Either (critical for FP libraries)
🔹 Supports higher-kinded abstractions cleanly

Use Case: Generic programming (e.g., Cats, ZIO).

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Comparative Analysis: Scala 2 vs Scala 3

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Final Thoughts

Scala 3 isn’t just an upgrade—it’s a leap forward in expressiveness and performance. Key takeaways:

1. Opaque types for zero-cost domain modeling.

2. Traits with parameters for better modularity.

3. Enums to eliminate boilerplate.

4. Type lambdas for advanced FP patterns.

These features make Scala 3 the best choice for building type-safe, high-performance systems.

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🎥 Want to Go Deeper?

DO CHECK THIS OUT:

LSUG July 2024 | Anatomy of Scaladex - Kannupriya Kalra

https://www.youtube.com/watch?v=8qWsSiLb08U

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🌟 A Special Thank You

Before I wrap up, I need to take a moment to express my gratitude to the incredible people who made this Scala journey possible.

First, to Daniel Ciocîrlan(Rock the JVM) – your course didn’t just teach me Scala; it rewired how I think about code. Thank you for:

• Demystifying functional programming with crystal-clear explanations

• Making advanced concepts like implicits and monads feel approachable

• Your contagious enthusiasm that made learning fun

• Most of all, for offering this world-class course for free (watch here)

To my amazing mentors Kannupriya Kalra and Adrien Piquerez – your guidance gave me the courage to tackle Scala head-on. Your patience with my endless questions and your belief in me kept me going when concepts got tough.

And to Scala Center – thank you for fostering such a welcoming community and creating resources that make Scala accessible to all. Your work empowers developers worldwide to embrace this beautiful language.

This wasn’t just about learning syntax – it was about joining a community that values elegant, expressive code. To everyone who helped along the way: You’ve changed how I write software forever.

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🎓 CERTIFICATE OF COMPLETION 🎓

✨Scala 3 New Features✨

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🔗 Useful Links:

🔸 My GSoC Project: Scaladex Compiler Plugin Support

🔸 GitHub: github.com/vidishagawas121

🔸 LinkedIn: Vidisha Gawas

🔸 Discord: reader_83216

🔸 Previous Post: Before GSoC: My Open Source Journey Begins and Community Bonding Experience at GSoC 2025

🔸Scala Discord Channel: Discord channel link