Nested parameterized types with Dart 1.22.0 new instantiate to bound rules

Question

I have an issue related to the new instantiate to bound rule in Dart 1.22.0. I have a BaseModel class that takes a parameterized type called ParentType that itself extends BaseModel.

Not all BaseModels have a specific ParentType, and if I instantiate BaseModel as the ParentType, then I get infinite rule breaking.

Here's an example:

abstract class BaseModel<ParentType extends BaseModel> {
    ParentType parentModel
}

class ParentModel extends BaseModel<BaseModel<...>> {}

class ChildModel extends BaseModel<ParentModel> {}

I’m going to be ignoring the rule for now as this issue hasn't seemed to have any impact on development.

score 2 · Answer 1 · answered Feb 17 '17 at 19:21

2

Depends a bit on what you want to accomplish, but assuming that you want ParentModel to be usable as any kind of BaseModel (where the parentModel field will always be null), then this may be what you want:

abstract class BaseModel<ParentType extends BaseModel<ParentType>> {
  ParentType parentModel;
}

class ParentModel extends BaseModel<Null> {}

class ChildModel extends BaseModel<ParentModel> {}

If not, I would need to know more about what the constraints and goals of your problem are.

answered Feb 17 '17 at 19:21

Leaf Petersen

141
2

This satisfies the analyzer for the basic example, but it breaks where I have more complex inheritance. `class ParentModel extends ChildModel` `class ChildModel extends BaseModel` My codebase is too large and complex to make all of these typing changes, and I don't see the benefit. I am resigned to ignoring the rule. I've struggled with strong mode in the past, which was the impetus to implement this pattern to begin with. Before this, I was overriding field types, which to me seems like a preferred solution. – Sam B Feb 17 '17 at 23:02

score 0 · Answer 2 · answered Feb 17 '17 at 17:56

0

This might do what you want:

abstract class BaseModel<ParentType extends BaseModel<Null>>

answered Feb 17 '17 at 17:56

Günter Zöchbauer

623,577
216
2,003
1,567

That seems to work for the very simple example, but it is not working for my more complex BaseModel relationships. – Sam B Feb 17 '17 at 18:32
Can you update your question with a concrete example? – Günter Zöchbauer Feb 17 '17 at 18:34

Nested parameterized types with Dart 1.22.0 new instantiate to bound rules

2 Answers2