Dart: Function X is NOT a subtype of Function Y

Question

In Dart, if:

MyWidget is of type Widget.

Then why:

(BuildContext, ViewModel) => MyWidget

is not a subtype of:

(BuildContext, dynamic) => Widget ?

And how do I fix this?

See https://stackoverflow.com/questions/1150372/confused-about-function-subtyping. — Jonah Williams, Jan 07 '19 at 05:04
@JonahWilliams This link perfectly answers my question. I'm coming from Java, where I never really had to think about function subtyping. — Marcelo Glasberg, Jan 07 '19 at 19:44

score 1 · Accepted Answer · answered Jan 07 '19 at 13:11

Because dynamic is a super-type of ViewModel, so a function accepting (BuildContext, ViewModel) as argument can't be used where a function accepting (BuildContext, dynamic) is required. The latter can be called with second arguments that are no ViewModel instances.

So, the problem is in the arguments, not in the return type.

Dart: Function X is NOT a subtype of Function Y

1 Answers1