3.x

Scala Native

Cats Effect supports Scala Native since 3.3.14.

Scala Native example

Here's an example of a Hello world project compiled to a native executable using sbt-scala-native plugin.

// project/plugins.sbt
addSbtPlugin("org.scala-native" % "sbt-scala-native" % "0.4.7")

// build.sbt
ThisBuild / organization := "com.example"
ThisBuild / scalaVersion := "2.13.8"

lazy val root = project.in(file("."))
  .enablePlugins(ScalaNativePlugin)
  .settings(
    name                := "cats-effect-3-hello-world",
    libraryDependencies += "org.typelevel" %%% "cats-effect" % "3.5.6",
    Compile / mainClass := Some("com.example.Main")
 )

// src/main/scala/com/example/Main.scala
package com.example

import cats.effect.{IO, IOApp}

object Main extends IOApp.Simple {
  def run: IO[Unit] = IO.println("Hello Cats Effect!")
}

The code can be compiled using sbt nativeLink and a native executable can then be found under target/scala-2.13/cats-effect-3-hello-world-out, and executed as any native executable with the benefit of a really fast startup time (hyperfine is a command line benchmarking tool written in Rust)

$ ./target/scala-2.13/cats-effect-3-hello-world-out
Hello Cats Effect!

$ hyperfine ./target/scala-2.13/cats-effect-3-hello-world-out
Benchmark 1: ./target/native-image/cats-effect-3-hello-world-out
  Time (mean ± σ):       7.5 ms ±   1.2 ms    [User: 3.6 ms, System: 2.3 ms]
  Range (min … max):     6.0 ms …  17.9 ms    141 runs

Another way to get your cats effect app compiled to a native executable is to leverage the package command of scala-cli, like in the example

Limitations

The Scala Native runtime is single-threaded, similarly to ScalaJS. That's why the IO#unsafeRunSync is not available. Be careful with IO.blocking(...) as it blocks the thread since there is no dedicated blocking thread pool. For more in-depth details, see the article with explanations of how the Native runtime works.

Showcase projects

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