Packages

trait IOApp extends AnyRef

App type that runs a cats.effect.IO. Shutdown occurs after the IO completes, as follows:

- If completed with ExitCode.Success, the main method exits and shutdown is handled by the platform.

- If completed with any other ExitCode, sys.exit is called with the specified code.

- If the IO raises an error, the stack trace is printed to standard error and sys.exit(1) is called.

When a shutdown is requested via a signal, the IO is canceled and we wait for the IO to release any resources. The process exits with the numeric value of the signal plus 128.

import cats.effect._
import cats.syntax.all._

object MyApp extends IOApp {
  def run(args: List[String]): IO[ExitCode] =
    args.headOption match {
      case Some(name) =>
        IO(println(s"Hello, ${name}.")).as(ExitCode.Success)
      case None =>
        IO(System.err.println("Usage: MyApp name")).as(ExitCode(2))
    }
}
Source
IOApp.scala
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Abstract Value Members

  1. abstract def run(args: List[String]): IO[ExitCode]

    Produces the IO to be run as an app.

    Produces the IO to be run as an app.

    returns

    the cats.effect.ExitCode the JVM exits with

Concrete Value Members

  1. final def !=(arg0: Any): Boolean
    Definition Classes
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  2. final def ##: Int
    Definition Classes
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  3. final def ==(arg0: Any): Boolean
    Definition Classes
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  4. final def asInstanceOf[T0]: T0
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  5. def clone(): AnyRef
    Attributes
    protected[lang]
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    Annotations
    @throws(classOf[java.lang.CloneNotSupportedException]) @native() @HotSpotIntrinsicCandidate()
  6. implicit def contextShift: ContextShift[IO]

    Provides an implicit ContextShift for the app.

    Provides an implicit ContextShift for the app.

    The default on top of the JVM is lazily constructed as a fixed thread pool based on number available of available CPUs (see PoolUtils).

    On top of JavaScript, the global execution context is used (i.e. scala.concurrent.ExecutionContext.Implicits.global).

    Users can override this value in order to customize the main thread-pool on top of the JVM, or to customize the run-loop on top of JavaScript.

    Attributes
    protected
  7. final def eq(arg0: AnyRef): Boolean
    Definition Classes
    AnyRef
  8. def equals(arg0: AnyRef): Boolean
    Definition Classes
    AnyRef → Any
  9. def executionContext: ExecutionContext

    Provides a default ExecutionContext for the app.

    Provides a default ExecutionContext for the app.

    The default on top of the JVM is lazily constructed as a fixed thread pool based on number available of available CPUs (see PoolUtils).

    On top of JavaScript, this will use the standard setTimeout.

    Attributes
    protected
    Note

    This is the same ExecutionContext that backs the default implicit ContextShift

    ,

    To use a different ExecutionContext, consider extending IOApp.WithContext, which will do it more comprehensively.

  10. final def getClass(): Class[_ <: AnyRef]
    Definition Classes
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    Annotations
    @native() @HotSpotIntrinsicCandidate()
  11. def hashCode(): Int
    Definition Classes
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    Annotations
    @native() @HotSpotIntrinsicCandidate()
  12. final def isInstanceOf[T0]: Boolean
    Definition Classes
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  13. def main(args: Array[String]): Unit

    The main method that runs the IO returned by run and exits the app with the resulting code on completion.

  14. final def ne(arg0: AnyRef): Boolean
    Definition Classes
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  15. final def notify(): Unit
    Definition Classes
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    @native() @HotSpotIntrinsicCandidate()
  16. final def notifyAll(): Unit
    Definition Classes
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    @native() @HotSpotIntrinsicCandidate()
  17. final def synchronized[T0](arg0: => T0): T0
    Definition Classes
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  18. implicit def timer: Timer[IO]

    Provides an implicit Timer for the app.

    Provides an implicit Timer for the app.

    Users can override this value in order to customize the underlying scheduler being used.

    The default on top of the JVM uses an internal scheduler built with Java's Executors.newScheduledThreadPool (configured with one or two threads) and that defers the execution of the scheduled ticks (the bind continuations get shifted) to the app's contextShift.

    On top of JavaScript the default timer will simply use the standard setTimeout.

    Attributes
    protected
  19. def toString(): String
    Definition Classes
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  20. final def wait(arg0: Long, arg1: Int): Unit
    Definition Classes
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    Annotations
    @throws(classOf[java.lang.InterruptedException])
  21. final def wait(arg0: Long): Unit
    Definition Classes
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    @throws(classOf[java.lang.InterruptedException]) @native()
  22. final def wait(): Unit
    Definition Classes
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    Annotations
    @throws(classOf[java.lang.InterruptedException])

Deprecated Value Members

  1. def finalize(): Unit
    Attributes
    protected[lang]
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    @throws(classOf[java.lang.Throwable]) @Deprecated
    Deprecated

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