Exit in Scala

Here’s an idiomatic Scala example demonstrating the concept of program exit:

import scala.sys.exit

object ExitExample {
  def main(args: Array[String]): Unit = {
    // This println will be executed
    println("Starting the program")

    // This will never be called due to the exit
    sys.addShutdownHook {
      println("This shutdown hook won't be executed")
    }

    // Exit with status 3
    exit(3)

    // This line will never be reached
    println("This won't be printed")
  }
}

This Scala program demonstrates how to exit a program with a specific status code. Let’s break it down:

1. We import scala.sys.exit to use the exit function.

2. We define an object named ExitExample with a main method, which is the entry point of our Scala program.

3. We print a message to show that the program has started.

4. We add a shutdown hook using sys.addShutdownHook. In Scala, unlike Go’s defer, shutdown hooks are typically used for cleanup operations. However, when using exit, these hooks are not guaranteed to run.

5. We call exit(3) to immediately terminate the program with status code 3.

6. The last println statement will never be executed because the program exits before reaching this line.

To run this program:

1. Save the code in a file named ExitExample.scala.
2. Compile the code using the Scala compiler:

$ scalac ExitExample.scala

3. Run the compiled program:

$ scala ExitExample
Starting the program

4. Check the exit status:

$ echo $?
3

Note that the shutdown hook message is not printed, and the exit status is 3 as specified.

In Scala, like in Java, the main method doesn’t return an exit code. Instead, we use sys.exit() to explicitly set a non-zero exit status. This is similar to Go’s os.Exit() functionality.

It’s important to use exit judiciously, as it immediately terminates the program without running cleanup code or finalizers. In most cases, it’s better to let your program terminate normally, allowing for proper resource cleanup.