Define an application that wires three components together.

Create the DI registry and connect it to a program:

  defines application
    MyApp
      register ConsoleLogger() as Logger
      register GreetingService() as Service

  defines program
    Main() with application of MyApp

'with application of' connects the program to the registry. All injection points resolve from this application.

See Q1110 for register/inject basics. See Q1111 for ordering.

Example

defines module qa.di.applicationregistry

  defines component

    Logger as abstract
      log() as abstract
        -> message as String
        <- output as String?
      default operator ?

    ConsoleLogger is Logger
      override log()
        -> message as String
        <- output as String: `[LOG] ${message}`
      default operator ?

    Formatter as abstract
      format() as abstract
        -> text as String
        <- result as String?
      default operator ?

    UpperFormatter is Formatter
      override format()
        -> text as String
        <- result as String: text.upperCase()
      default operator ?

    Service as abstract
      greet() as abstract
        -> name as String
        <- greeting as String?
      default operator ?

    GreetingService is Service
      logger as Logger!
      formatter as Formatter!

      override greet()
        -> name as String
        <- greeting <- String()
        formatted <- formatter.format(name)
        greeting: logger.log(formatted)

      default operator ?

  defines application

    GreetApp
      register ConsoleLogger() as Logger
      register UpperFormatter() as Formatter
      register GreetingService() as Service

  defines program

    ApplicationRegistryDemo() with application of GreetApp
      stdout <- Stdout()
      service as Service!
      result <- service.greet("World")
      stdout.println(result)

Common mistakes

E08220 — A program that uses DI injection must be linked to its application with 'with application of AppName' (EK9 has no wiring annotations). See ek9 -h E08220 for details.

Incorrect:

ApplicationRegistryDemo()

Correct:

ApplicationRegistryDemo() with application of GreetApp

Other ways to ask this

I need an application block that registers Logger, Formatter, and Service
In Spring I'd use @Configuration with @Bean methods. Write the EK9 application
Given three components with dependencies, define the application wiring
Set up a complete application registry with multiple registrations

Coming from another language?

Spring: @SpringBootApplication + @Configuration. Guice: AbstractModule.configure(). .NET: Program.cs with builder.Services. EK9: defines application with register statements.

Keywords: registry, register, wire, DI, application, configuration