Simple scala.swing application fails - scala

Question

I am using scalas to run a simple scala.swing application:
#!/usr/bin/env scalas
/***
scalaVersion := "2.12.6"
libraryDependencies += "org.scala-lang.modules" %% "scala-swing" % "2.1.1"
*/
import scala.swing._
object FirstSwingApp extends SimpleSwingApplication {
def top = new MainFrame {
title = "First Swing App"
contents = new Button {
text = "Click me"
}
}
}
This compiles and runs (on OSX 10.14), but there is no visible output; the process just terminates after a few seconds. What have I done wrong?

Answer 1

Judging from this documentation https://www.scala-sbt.org/release/docs/Scripts.html - scalas doesn't work like java -jar ..., that is, it isn't running your main class in some object.
It merely executes code as if it was REPL, so if you want to execute code, run it yourself:
#!/usr/bin/env scalas
/***
scalaVersion := "2.12.6"
libraryDependencies += "org.scala-lang.modules" %% "scala-swing" % "2.1.1"
*/
import scala.swing._
// creates object but doesn't run anything
object FirstSwingApp extends SimpleSwingApplication {
def top = new MainFrame {
title = "First Swing App"
contents = new Button {
text = "Click me"
}
}
}
FirstSwingApp.main(new Array[String](0)) // run main manually, or whatever you prefer