Create a Logger component with a name field and a log method.

Define a component with fields and methods:

  defines component
    Logger
      name <- "DefaultLogger"
      log()
        -> message as String
        <- output as String: name + ": " + message

Components are DI-managed types with fields, constructors, methods, and operators.

See Q227 for compile-time DI validation. See Q1110 for register and inject.

Example

defines module qa.di.definecomponent

  defines component

    Logger
      name <- "AppLogger"

      getName()
        <- rtn as String: name

      log()
        -> message as String
        <- output as String: `${name}: ${message}`

      default operator

  defines program

    DefineComponentDemo()
      stdout <- Stdout()

      logger <- Logger()
      result <- logger.log("Application started")
      stdout.println(result)
      stdout.println(`Logger name: ${logger.getName()}`)

Common mistakes

E01010 — EK9 has no annotations. Use 'defines component' to declare DI-managed types.

Incorrect:

  defines class
    @Component Logger

Correct:

defines component

    Logger

Other ways to ask this

I need to define a reusable service component with fields and methods
In Spring I'd use @Component on a class. Write the EK9 equivalent
Given a logging service, define it as a component with state and behaviour
Build a basic component that holds configuration and provides a method

Coming from another language?

Spring: @Component class. Guice: bind(Logger.class). .NET: services.AddSingleton<Logger>(). EK9: defines component + register in application.

Keywords: define, component, fields, methods, service, DI