E2589 Helper type can not be declared in parameterized type context (Object Pascal)
This occurs whenever you try to declare a helper type for a parameterized type.
type TFoo<T> = class type TFooHelper = class helper for TFoo<T> end; end; end.
This can be solved by removing the parameterized type context, as follows:
type TFoo = class type TFooHelper = class helper for TFoo end; end; end.