App

scala.App

The App trait can be used to quickly turn objects into executable programs. Here is an example:

object Main extends App {
  Console.println("Hello World: " + (args mkString ", "))
}

No explicit main method is needed. Instead, the whole class body becomes the “main method”.

args returns the current command line arguments as an array.

Caveats

It should be noted that this trait is implemented using the DelayedInit functionality, which means that fields of the object will not have been initialized before the main method has been executed.

Future versions of this trait will no longer extend DelayedInit.

In Scala 3, the DelayedInit feature was dropped. App exists only in a limited form that also does not support command line arguments and will be deprecated in the future.

@main methods are the recommended scheme to generate programs that can be invoked from the command line in Scala 3.

@main def runMyProgram(args: String*): Unit = {
  // your program here
}

If programs need to cross-build between Scala 2 and Scala 3, it is recommended to use an explicit main method:

object Main {
  def main(args: Array[String]): Unit = {
    // your program here
  }
}

Attributes

Source: App.scala
Graph
Supertypes: trait DelayedInit

class Object

trait Matchable

class Any

Members list

Value members

Concrete methods

The command line arguments passed to the application's main method.

Attributes

Source: App.scala

The main method.

The main method. This stores all arguments so that they can be retrieved with args and then executes all initialization code segments in the order in which they were passed to delayedInit.

Value parameters

args: the arguments passed to the main method

Attributes

Source: App.scala

Deprecated methods

The init hook.

The init hook. This saves all initialization code for execution within main. This method is normally never called directly from user code. Instead it is called as compiler-generated code for those classes and objects (but not traits) that inherit from the DelayedInit trait and that do not themselves define a delayedInit method.

Value parameters

body: the initialization code to be stored for later execution

Attributes

Deprecated: [Since version 2.11.0] the delayedInit mechanism will disappear
Definition Classes: DelayedInit
Source: App.scala

Concrete fields

The time when the execution of this program started, in milliseconds since 1 January 1970 UTC.

Attributes

Source: App.scala

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