E06090: a named dynamic class cannot be used within a generic type/function

What went wrong

Named dynamic classes cannot be defined inside generic types or functions. Use anonymous dynamic classes (assign to variable) or define named classes outside the generic context.

Worked examples

Compilable examples demonstrating this error and the correct fix:

• ek9 -q 648 (Why cannot I use named dynamic classes inside a generic t...)

Rationale

Named types inside generics create ambiguity about type scope and parameterization. When a generic is instantiated with different type parameters, named inner classes would create conflicting type definitions. Anonymous dynamic classes avoid this by having no name to conflict.

How to fix it

1. Remove the type name from dynamic class: use 'helper <- ()' not 'MyHelper <- ()'
2. Or define named classes outside the generic scope
3. Reference external named types from within generics

Key syntax difference

WRONG: MyHelper <- () is Interface as class // Named - creates type RIGHT: helper <- () is Interface as class // Anonymous - just a variable

Common causes

• Wanting to name a type for clarity (use comments instead)
• Habit from languages allowing named inner classes
• Not realizing lowercase is variable name, not type name

See also

• E06090: named dynamic class in generic (this error)
• E06100: abstract generic function (related generic restriction)

Examples

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

Fails with E06090: a named dynamic class cannot be used within a generic type/function

#!ek9
defines module error.e06090.bad

  defines trait

    Processor
      process()
        -> text as String
        <- rtn as String: text

  defines class

    Container of type T

      handle()
        -> item as T
        <- rtn as String?
        require item?

        //A NAMED dynamic class would be one class shared by every 'Container of X'
        processor as Processor: NamedProcessor() with trait of Processor as class
          override process()
            -> text as String
            <- rtn as String: `processed: ${text}`

        rtn: processor.process("item")

Fixed: Leave the dynamic class anonymous inside a generic type or function

#!ek9
defines module error.e06090.good

  defines trait

    Processor
      process()
        -> text as String
        <- rtn as String: text

  defines class

    Container of type T

      handle()
        -> item as T
        <- rtn as String?
        require item?

        processor as Processor: () with trait of Processor as class
          override process()
            -> text as String
            <- rtn as String: `processed: ${text}`

        rtn: processor.process("item")

Questions and answers

These Q&A entries show E06090 and its fix:

• Q648: Why cannot I use named dynamic classes inside a generic type definition?