E07810: Dispatch only supported in classes

What went wrong

You're using 'dispatcher' keyword outside of a class context. Dispatch (multiple dispatch pattern) is only supported in classes.

Worked examples

Compilable examples demonstrating this error and the correct fix:

• ek9 -q 106 (What are traits and how do I use them in EK9?)

How to fix it

1. Move dispatcher method to a class
2. Dispatch pattern requires class instance context

Common causes

• Dispatcher in function
• Dispatcher in trait

See also

• E07810: dispatcher outside class (this error)
• E07820: multiple dispatchers in class

Examples

Every example is compiled by the EK9 compiler: the first fails exactly as captioned, the others fix it.

Fails with E07810: Dispatch only supported in classes

#!ek9
defines module error.e07810.bad

  defines trait

    Describer

      //Dispatch chooses a method on a class's actual argument types
      describe() as dispatcher
        -> shape as Shape
        <- rtn as String: shape.kind()

  defines class
    Shape as open
      kind()
        <- rtn as String: "shape"

Fixed: Put the dispatcher on a class

#!ek9
defines module error.e07810.good

  defines class

    Shape as open
      kind()
        <- rtn as String: "shape"

    Circle extends Shape
      override kind()
        <- rtn as String: "circle"

    Describer
      describe()
        -> circle as Circle
        <- rtn as String: "a round " + circle.kind()

      describe() as dispatcher
        -> shape as Shape
        <- rtn as String: "some " + shape.kind()

Questions and answers

These Q&A entries show E07810 and its fix:

• Q106: What are traits and how do I use them in EK9?