arguments in combiner need type info

[mikew]

I'm new to Dart, so this could be just a language quirk, but the examples in the readme don't provide give any type info to the arguments in the combiner function. When doing that, they're actually dynamic, inference doesn't work.

Given this:

class ExampleState {
  String firstName;
  String age;
}

final getFirstName = (ExampleState state) => state.firstName;
final getAge = (ExampleState state) => state.age;

Here is what the readme says to do:

final exampleSelector = createSelector2(
  getFirstName,
  getAge,
  (firstName, age) => '$firstName $age',
);

But firstName and age are dynamic, providing type info works but results in duplication:

final exampleSelector = createSelector2(
  getFirstName,
  getAge,
  (String firstName, int age) => '$firstName $age',
);

What's worse is when you give the wrong type info, Dart suddenly smartens up and says it can't happen:

final exampleSelector = createSelector2(
  getFirstName,
  getAge,
  (String firstName, String age) => '$firstName $age',
);

yields:

Couldn't infer type parameter 'R2'.

Tried to infer 'int' for 'R2' which doesn't work:
  Parameter 'combiner' declared as     '(R1, R2) → T'
                       but argument is '(String, String) → String'.
The type 'int' was inferred from:
  Parameter 'selector2' declared as     '(S) → R2'
                        but argument is '(ExampleState) → int'.

Consider passing explicit type argument(s) to the generic.
dart(strong_mode_could_not_infer)

Could this have something to do with my analysis_options.yaml file? Or is Dart's inference nowhere near the level in TypeScript?

[NicolasCharpentier]

Hey @mikew I'm like you at the time, new to Dart. Two years later this issue has not been treated and also bothers me, but it does not look like it can be fixed.

See dart-lang/sdk#34408 where it seems like Dart team won't fix that soonly.