Pass a dynamic class as a function argument.

Pass a dynamic class to a function as the trait type:

  myObj <- (label) with trait of Describable as class
    override describe() as pure <- rtn as String: label
    default operator ?
  printDescription(myObj)

The function receives it as Describable -- it does not know or care that it is a dynamic class.

See Q1126 for dynamic class basics. See Q1125 for dynamic functions.

Example

defines module qa.advancedtypes.dynamicclassasargument

  defines trait

    Describable
      describe() as pure abstract
        <- rtn as String?

  defines function

    printDescription()
      -> item as Describable
      <- output as String: item.describe()

  defines program

    DynamicClassAsArgumentDemo()
      stdout <- Stdout()
      label <- "Widget"

      //Create dynamic class implementing Describable
      widget <- (label) with trait of Describable as class
        override describe() as pure
          <- rtn as String: label
        default operator ?

      //Pass it to a function that takes the trait type
      result <- printDescription(widget)
      stdout.println(result)

Common mistakes

E01075 — EK9 has no 'new' keyword; instantiate a type directly as TypeName() (or build a dynamic class first and pass that). See ek9 -h E01075 for details.

Incorrect:

printDescription(new Describable())

Correct:

printDescription(widget)

Other ways to ask this

I need to create an inline trait implementation and pass it to a function
In Java I'd pass an anonymous class to a method. Write the EK9 equivalent
Given a function that takes a Describable, create and pass a dynamic implementation
Build a dynamic class inline at the call site and pass it directly

Coming from another language?

Java: printDescription(new Describable() { ... }). Kotlin: printDescription(object : Describable { ... }). EK9: create dynamic class, pass as trait type.

Keywords: argument, dynamic, class, pass, function, inline