Unified way to create a single main entrypoint that supports argument parsing and multiple commands. Create tasks that can be delegated to
Tasks are easy to make, they serve as individual "mains" that can be delegated to:
As an example from Carlyle
object App extends TaskEnabledApp {
DateTimeZone.setDefault(DateTimeZone.UTC)
override def appName: String = "carlyle"
override def tasks: List[Task] = List(new ServerTask(), new MigrateDbTask)
}Where each task looks like:
case class ServerConfig(
metricsEnabled: Boolean = true
)
class ServerTask()(implicit executionContext: ExecutionContext) extends Task {
override type Config = ServerConfig
override def emptyConfig: ServerConfig = ServerConfig()
override def definition: TaskDefinition[ServerConfig] = {
new TaskDefinition[ServerConfig](
name = "server",
description = "Server",
args =
_.opt[Unit]("disableMetrics").
action((_, config) => {
config.copy(metricsEnabled = false)
})
)
}
override def execute(args: ServerConfig): Unit = {
new Server(Modules(args.metricsEnabled)).main(Array.empty)
}
}class MigrateDbTask extends Task {
override type Config = Unit
override def emptyConfig: Unit = Unit
override def definition: TaskDefinition[Unit] = {
TaskDefinition(
name = "migrate-db",
description = "Migrates the carlyle db or creates a new one"
)
}
override def execute(args: Unit): Unit = {
val migrator = Modules().injector().make[Migrator]
migrator.migrate()
}
}Here we have an app that defines 2 tasks. If we run this app with no arguments we'll get:
Error: Command required
Usage: carlyle [server|migrate-db] [options]
Command: server
Server
Command: migrate-db
Migrates the carlyle db or creates a new one
--help prints this usage text
Select a command to run. Each command may have subcommands.
If we run a command any unknown command (-h is fine):
$ docker run -it paradoxical/carlyle server -h
Error: Unknown option -h
Usage: server [options]
--disableMetrics
You can now see that the server task is configured to accept an optional --disableMetrics command line argument.
In this way each task can define its own arguments and the main acts as a dispatcher given the root command.