Author | Lightnews

Haoyi Li is a software engineer and a core contributor to the Scala ecosystem. He's built a whole suite of Scala libraries under the com.lihaoyi banner, focusing on simplicity and productivity, as well as the Mill build tool, which he has since expanded beyond Scala to support other JVM tools like Java and Kotlin and experimental support for other things like TypeScript and Android, and promises better performance and user friendliness than Gradle and Maven can ever match. He's also the author of the book Hands-on Scala Programming, which focuses on getting things done with Scala. My own course, Scala Projects, uses Haoyi's book examples as starting points for full-fledged, shippable projects that you can use for yourself or turn into products: https://rockthejvm.com/courses/scala-projects Timeline 0:00 Intro 1:08 Conference tour 8:20 Haoyi's work on Mill 13:55 What Mill does better than other tools 18:48 Picking a config language 21:53 Scala at scale at Databricks 29:20 How Scala can continue innovating 34:50 Increasing industry adoption of Scala 39:45 Misconceptions about Scala 42:39 Haoyi's experience switching between IC - tech lead - manager - IC 49:39 How Haoyi started programming and why Scala stood out 57:08 Scala differentiators for the future 1:01:05 How Haoyi maintains his OSS library ecosystem 1:06:43 Hands-On Scala Programming: writing, publishing, open-sourcing 1:14:40 Haoyi's current and future contributions to Scala 1:18:16 Discussion on AI agents 1:29:54 Parting thoughts

Matej Cerny @matejcerny.bsky.social · 12h

There are so many great thoughts, to pinpoint just a few:
1️⃣ Tooling is nowhere near other languages
2️⃣ Missing a true "Spring Boot-like" framework
3️⃣ Official docs need real-world examples
4️⃣ The persistent misconception that "you need async for performance"
#scala youtu.be/a-uME7QBlxg

YouTube

Matej Cerny @matejcerny.bsky.social · 22h

This is probably the most complete tutorial on typeclasses in Scala 3, it's basically a short book. Bookmark it, as it has everything: givens, derivation, mirrors, inline defs, macros... you name it. #scala kubuszok.com//2025/sanely...

Don't look down! Look at the data instead!

Matej Cerny @matejcerny.bsky.social · 1d

After years, I came to the same conclusion: it's worth taking the time to use proper test data, even for attributes you don't currently use in your business logic. It'll save you so much time later. etorreborre.blog/dont-look-do...

You might get the same vertigo

etorreborre.blog

Scala vs F# - Alexandru Nedelcu

Matej Cerny @matejcerny.bsky.social · 1d

Scala vs. F#: Which is more functional? #scala #fsharp alexn.org/blog/2025/11...

Which language leans more towards functional programming? In this binary choice, people have perceived F# to be that language, due to its ML roots, but I have a different perspective…

alexn.org

Matej Cerny @matejcerny.bsky.social · 2d

The tech industry is creating its own talent crisis. By ditching junior devs for AI hype, companies are just burning out their seniors and killing the future talent pipeline. #ai www.youtube.com/watch?v=DcJ5...

Dev will really suck in a few years...

www.youtube.com

Matej Cerny @matejcerny.bsky.social · 3d

Binary compatibility is a very important topic that every senior should understand. This video, even though it's about Smithy4s, explains concepts for evolving a library's schema in a binary-compatible way. #scala youtu.be/1HFV-tGZVlY

Deep dive: how I added THIS feature to smithy4s (bincompat-friendly mode)

Matej Cerny @matejcerny.bsky.social · 5d

The most comprehensive collection of Scala learning material finally on YouTube. A freaking 283 videos! #scala www.youtube.com/@Ziverge/pla...

Release v0.23.33 · http4s/http4s · GitHub

Matej Cerny @matejcerny.bsky.social · 5d

Respect to Dylan Halperin for his massive contribution to @http4s! 🚀 His new MultipartReceiver is in the latest version after over a year of review, adding safer, fail-fast file uploads with size limits and no buffering. #scala github.com/http4s/http4...

What's Changed http4s-core fix: proxy authorization header instantiation with basic credentials by @tpetillot in #7742 Introduce MultipartReceiver for custom, fail-fast multipart decoding by @dyle...

github.com

Benchmarking Postgres 17 vs 18 — PlanetScale

Matej Cerny @matejcerny.bsky.social · 5d

I was really looking forward to io_uring in Postgres 18, but it turns out it's not the winning I/O strategy. Worker, the new default, seems to be the best all-around method so far, performing well on all storage types. #postgres planetscale.com/blog/benchma...

Postgres 18 brings a significant improvement to read performance via async I/O and I/O worker threads. Here we compare its performance to Postgres 17.

planetscale.com

Matej Cerny @matejcerny.bsky.social · 6d

Java is removing sun.misc.Unsafe, an API which is widely used but was never supported or meant to be public. This is one of the reasons for the adoption of JDK 17 in the upcoming version of Scala, which relies on Unsafe for its lazy val implementation. #java #scala youtu.be/jCbqkMKegmY

JEP Explained. JEP 471: Deprecate the Memory-Access Methods in sun.misc.Unsafe for Removal

YouTube video by IntelliJ IDEA, a JetBrains IDE

Scala 3 / Match Types - Alexandru Nedelcu

3

Matej Cerny @matejcerny.bsky.social · 7d

💡 Quick tip: Stop parsing Array[String], use @main and get type-safe command-line args directly as function parameters. #scala

1 4

Matej Cerny @matejcerny.bsky.social · 8d

Match types, an awesome feature which I haven't properly used yet 😀 #scala alexn.org/blog/2025/10...

Scala has a neat new feature, resembling TypeScript’s “conditional types”, but more powerful.

alexn.org

3

Matej Cerny @matejcerny.bsky.social · 9d

Taking bets on when Spark will adopt Scala 3. Just by reading the PR, my guess is never. 😔 #scala #spark github.com/apache/spark...

Enable -Xsource:3 compiler flag by joan38 · Pull Request #50474 · apache/spark · GitHub

What changes were proposed in this pull request? Enable -Xsource:3-cross compiler flag for future migration to Scala 3. https://docs.scala-lang.org/scala3/guides/migration/tooling-scala2-xsource3....

github.com

Reddit - The heart of the internet

Matej Cerny @matejcerny.bsky.social · 12d

Behold! The mythical Scala.js job offer is real! www.reddit.com/r/scala/comm... #scala

www.reddit.com

Matej Cerny @matejcerny.bsky.social · 13d

If you are able to represent an illegal state in your code, you should rethink your model. Start with these two simple tips 👇 www.yannmoisan.com/make-illegal... #ddd #scala

Ranking Enums in Programming Languages

Matej Cerny @matejcerny.bsky.social · 14d

Scala 3 would obviously also go in the S tier. #scala youtu.be/7EttvdzxY6M

Trezor Safe 7 | Bitcoin-only Hardware Wallet With TROPIC01 Chip

Matej Cerny @matejcerny.bsky.social · 15d

The first Trezor with a custom-built secure element is out! What a piece of tech - Bluetooth, a special LiFePO battery with Qi2 charging, a display with 520x380 resolution, an aluminium body and an IP54 rating 🤯 #bitcoin trezor.io/trezor-safe-...

Secure your bitcoin with Trezor Safe 7—Bluetooth, high-res color touchscreen & quantum-ready security.

trezor.io

Matej Cerny @matejcerny.bsky.social · 15d

I have my first on-call shift actually 😀

Matej Cerny @matejcerny.bsky.social · 15d

🎉 Scala 3.3.7 was quietly released last week with a backported fix for Android development, improved coverage reports, hashcodes of enums, and more. #scala github.com/scala/scala3...

Release 3.3.7 · scala/scala3 · GitHub

Highlights of the release Warn a standard interpolator used toString on a reference type with -Wtostring-interpolated #20578 Unblock Scala 3 on Android #22632 Implement :jar (deprecate :require) i...

github.com

Matej Cerny @matejcerny.bsky.social · 15d

Why use a dedicated k8s operator setup when you can spend two days building your own webhook-based version in Scala? 😂 Anyway, it was a great read! #scala blog.indoorvivants.com/2025-10-20-r...

Matej Cerny @matejcerny.bsky.social · 16d

What a day to have my first on-call shift 😀 #awsoutage

Matej Cerny @matejcerny.bsky.social · 18d

With all the attention on the official Windows release, I completely missed the new settings UI editor. Zed team's velocity is abnormal 🤯

Zed @zed.dev · 18d

By default, you'll be greeted by a friendly new window when opening Zed's settings. No more JSON, unless you're into that type of thing!

Matej Cerny @matejcerny.bsky.social · 19d

What a release! 🎉 127 pull requests have been merged from 18 contributors. Check out the feature tour 👇 #scala

Scala Space @scalaspace.bsky.social · 20d

New Metals 1.6.3, codename "Osmium", has just been released!

It comes with few interesting new features and we'll take the opportunity to go on a small tour.

My golang guilty pleasure: ADTs - by Hugo Sousa

Matej Cerny @matejcerny.bsky.social · 20d

Go is really a toy language.🧸 #golang statelessmachine.com/p/my-golang-...

Golang is designed as a quite open language.

statelessmachine.com