Create an aspect that takes a label in its constructor for identification.

← Design Patterns and Idioms · Ref: Q1116

Aspects are classes with constructors and fields:

  LabelledAspect extends Aspect
    label <- String()
    LabelledAspect()
      -> label as String
      this.label :=: label
  ...
  register Impl() as Abstract with aspect of LabelledAspect("audit")

Pass constructor arguments at registration time.

See Q1115 for basic aspect. See Q1117 for exception handling.

Example

defines module qa.designpatterns.aspectconstructor

  defines component

    Printer as abstract
      print()
        <- rtn as String: "AbstractPrinter"

    ConcretePrinter is Printer
      override print()
        <- rtn as String: "ConcretePrinter"

  defines class

    LabelledAspect extends Aspect
      label <- String()

      LabelledAspect()
        -> label as String
        this.label :=: label

      default operator ?

  defines application

    AspectConstructorApp
      register ConcretePrinter() as Printer with aspect of LabelledAspect("audit")

  defines program

    AspectConstructorDemo() with application of AspectConstructorApp
      stdout <- Stdout()
      printer as Printer!
      result <- printer.print()
      stdout.println(result)

Other ways to ask this

I need an aspect with configurable state passed through its constructor
In Spring AOP I'd use @Aspect with fields. Write the EK9 aspect with constructor args
Given an aspect that needs a name, pass it via the constructor at registration
Build a parameterised aspect that carries configuration

Coming from another language?

Spring AOP: @Aspect class with @Value injection. AspectJ: aspect with constructor. EK9: Aspect subclass with constructor, configured at registration.

Keywords: AOP, constructor, configuration, parameters, aspect