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Jakub Kozłowski kubukoz

I might take a week to respond. Or a month.
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View on tf and zio in

Why you prefer cats instead of zio? TF? It’s looks like zio ecosystem more widely and zio 2.0 has better performance What do you think?

Great question!

Performance-wise, it really depends on what you're doing. The problem with benchmarks (including the ones posted for ZIO and Cats Effect) is that they apply only to abstract situations, which are often nothing like what you see in real applications. A great write-up on this problem by Daniel Spiewak here, he wrote it better than I ever could:

Also, this is not an app meant for production - I don't care that much about performance under load because there will be no load. And individual operations will often be bounded by I/O anyway, so the efficiency of the underlying runtime is likely not going to make a noticeable difference in use. Then again, both the client and server are JVM apps, so even the start-up penalty of the client will slow us down than picking even the least efficient e

View macroz.scala
// using scala 3.1.0
object macroz {
inline def foo(arg: Any): Unit = {
scala.compiletime.error("what is " + scala.compiletime.codeOf(arg))
View test.scala
import $ivy.`org.typelevel::cats-effect:3.2.9`
import cats.effect._
object Main extends IOApp.Simple {
def run: IO[Unit] = IO.println("hello Nix!")
kubukoz /
Created Oct 5, 2021
Semiauto vs auto derivation

You mention that you would only use circe auto derivation in only a few limited cases - may I ask why? It looks like you are using semi-auto derivation instead. Why is this better/more stable?

The difference is where the derivation happens - in semiauto, you only have one place where a codec for a given type will be derived: at definition site, which is usually the companion object (it's the companion object in our case, but it could be anywhere really - point still stands that it's easier to track). In auto derivation, codecs are derived as needed by the usage - e.g. in the endpoint definitions or in a controller (depending on the tech stack you use). The problem here is that you need all the codecs of all the fields and all their fields (...and so on...) to be available there.

The centralization of the codecs in Semiauto mode allows us to switch to a different format at any time, while keeping the representation consistent across all usages of it. Additionally, it allows us to test the codec logic witho

kubukoz / named_macro.scala
Created Sep 2, 2021
example of a `named` macro in Scala
View named_macro.scala
def demo = {
def foo(a: Int, b: Int) = s"foo(a = $a, b = $b)"
val a = 42
val b = 50
Macros.named(foo(b, a))
kubukoz / ReplaceFirstInTuple.scala
Created Jun 21, 2021
ReplaceFirstInTuple with shapeless
View ReplaceFirstInTuple.scala
import shapeless._
import shapeless.ops.tuple._
trait ReplaceFirstInTuple[Head, Replacement, Tup, TupReplaced] {
def replace(ik: Tup, j: Replacement): TupReplaced
def first(ik: Tup): Head
object ReplaceFirstInTuple {
kubukoz / Show.scala
Created May 21, 2021
Deriving a nice Show in scala 3
View Show.scala
import scala.deriving.*
import scala.compiletime.*
trait Show[T]:
extension (t: T) def show: String
given Show[String] = s => s
given Show[Int] = _.toString
object Show:
kubukoz / TraverseK.scala
Last active May 20, 2021
Deriving typeclass instances for higher-kinded type in Scala 3
View TraverseK.scala
// This could be very useful for
trait TraverseK[Alg[_[_]]]:
def traverseK[F[_], G[_]: Applicative, H[_]](alg: Alg[F])(fk: F ~> ([a] =>> G[H[a]])): G[Alg[H]]
def sequenceK[F[_]: Applicative, G[_]](alg: Alg[[a] =>> F[G[a]]]): F[Alg[G]] =
View valuesOf.scala
import scala.deriving.*
import scala.compiletime.*
inline def valuesOf[T <: Tuple]: List[String] = inline erasedValue[T] match {
case _: EmptyTuple => Nil
case _: (h *: t) =>
erasedValue[h] match {
case label: String =>
label :: valuesOf[t]
View Labels.scala
trait Labels[S] {
def label(v: S): String
object Labels {
import scala.deriving.*
import scala.compiletime.*
inline def derived[T](using s: Mirror.SumOf[T]): Labels[T] =