Inline functions parameter type override

[jacehensley-wf]

In Dart 2 I am seeing infos about some typing (uses_dynamic_as_bottom) and I don't know how I would get around it.

Basically I have something like:

new A()
  ..func = (int a) {};

Where A.func is of typeFunction(dynamic a)

If I make it Function(Object a) then it becomes an error:

"A value of type '(int) → Null' can't be assigned to a variable of type 'Function(Object) → dynamic'."

I put together a dartpad of a few things to try and make something work and clarify some rules for myself, but I couldn't find a way to make inline functions like that work.

https://dartpad.dartlang.org/22a4849f9f0d2fcd3813024df252adf0

Thanks!

[vsmenon]

We took a mis-step here. Our intent is to make dynamic in your example work like Object - i.e., a static error.

Details here:

#29630

[jacehensley-wf]

Oh okay, that makes sense. So should I type the parameters to Null?

[vsmenon]

For A.func? I think that would work.

@leafpetersen

[leafpetersen]

Making A.func typed to take Null will allow any unary function to be assigned to it. Note though that you will need to cast it to a different function type (or use a dynamic call) to call it then with anything except Null. That is:

Function(Null) f = (int x) => x + 1;
f(3); // This will fail, because of an implied downcast of `3` to `Null`
(f as Function(int))(3); // This will work
(f as dynamic)(3); // This will work.

[jacehensley-wf]

you will need to cast it to a different function type

That shows as an unnecessary cast info

---

So is there no "bottom" type that isn't null? Something like "Anything"? Because typing the parameter to Object doesn't work and neither does dynamic.

Function(Object) f2 = (int x) => x + 1; // warning
f2(3);
(f2 as Function(int))(3);
(f2 as dynamic)(3);
  
Function(dynamic) f3 = (int x) => x + 1; // info
f3(3);
(f3 as Function(int))(3);
(f3 as dynamic)(3);

[leafpetersen]

That shows as an unnecessary cast info

Bug. Filed it here #30897 .