E06220: choose either empty parenthesis '( )' with values or a type definition

What went wrong

You're mixing two incompatible approaches: providing constructor VALUES and explicitly specifying the generic TYPE. EK9 requires you choose ONE:

• Provide values → compiler INFERS type
• Specify type explicitly → use empty '()' constructor

Worked examples

Compilable examples demonstrating this error and the correct fix:

• ek9 -q 196 (How do I define generics with multiple type parameters in...)

Rationale

If you provide constructor arguments, the compiler infers the type from them. Specifying type explicitly would be either redundant (same type) or contradictory (different type). EK9 requires clear intent.

How to fix it

1. Remove 'of Type' and let compiler infer from values
2. Or remove values and use empty '()' with explicit type
3. Never combine both approaches

Common causes

• Trying to be "extra explicit" by providing both type and values
• Misunderstanding type inference vs explicit typing
• Coming from languages that allow both

See also

• E06220: values AND explicit type together (this error)
• E06200: '()' in type position
• E06210: missing '()' in instantiation position

Examples

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

Fails with E06220: choose either empty parenthesis '( )' with values or a type definition

#!ek9
defines module error.e06220.bad

  defines class

    Holder of type T
      item as T: T()

      default Holder()

      Holder()
        -> initial as T
        item: initial

      default operator ?

  defines function

    mixed()
      //An argument already says what T is; 'of Integer' says it again
      holder <- Holder(32) of Integer

Fixed: Let the argument give the type: Holder(32) is a Holder of Integer

#!ek9
defines module error.e06220.good

  defines class

    Holder of type T
      item as T: T()

      default Holder()

      Holder()
        -> initial as T
        item: initial

      default operator ?

  defines function

    inferred()
      <- rtn as Boolean?
      holder <- Holder(32)
      rtn: holder?

Fixed: Or construct with no argument and name the type

#!ek9
defines module error.e06220.good.explicit

  defines class

    Holder of type T
      item as T: T()

      default Holder()

      Holder()
        -> initial as T
        item: initial

      default operator ?

  defines function

    explicit()
      <- rtn as Boolean?
      holder <- Holder() of Integer
      rtn: holder?

Questions and answers

These Q&A entries show E06220 and its fix:

• Q196: How do I define generics with multiple type parameters in EK9?