Create a dynamic class with multiple methods implementing a trait inline.

Override multiple abstract methods in a dynamic class:

  obj <- () with trait of Speaker as class
    override greet() as pure
      <- rtn as String: "Hello"
    override farewell() as pure
      <- rtn as String: "Goodbye"
    default operator ?

Every abstract method in the trait must be overridden in the dynamic class body.

See Q1125 for dynamic functions. See Q1126 for dynamic class with capture.

Example

#!ek9
defines module qa.advancedtypes.dynamicclassmethods

  defines trait

    Speaker
      greet() as pure abstract
        <- rtn as String?
      farewell() as pure abstract
        <- rtn as String?

  defines program

    DynamicClassMethodsDemo()
      stdout <- Stdout()

      speaker <- () with trait of Speaker as class
        override greet() as pure
          <- rtn as String: "Hello"
        override farewell() as pure
          <- rtn as String: "Goodbye"
        default operator ?

      stdout.println(speaker.greet())
      stdout.println(speaker.farewell())

Common mistakes

E01075 — EK9 has no 'new' keyword — instantiate a type by calling its constructor directly, e.g. Stdout(). See ek9 -h E01075 for details.

Incorrect:

      stdout <- new Stdout()

Correct:

      stdout <- Stdout()

Other ways to ask this

I need an inline class that implements two abstract methods from a trait
In Java I'd use an anonymous class with multiple method overrides. Write the EK9 way
Given a trait with greet() and farewell(), create a one-off inline implementation
Build a dynamic class that overrides multiple trait methods

Coming from another language?

Java: anonymous inner class with multiple method overrides. Kotlin: object expression. Python: lambda (single method only). EK9: dynamic class implementing full trait.

Keywords: class, dynamic, inline, methods, multiple, trait