Dart Annotation - Unable to pass non constant method

Question

How can I pass-in non-constant method in Dart Annotations?

Here is my annotation:

class Injectable {
  final String name;
  final Scope scope;
  final List<Provider>? provider;

  const Injectable({this.name = '', this.scope = Scope.factory, this.provider});
}


class Provider<T> {
  final Type? useClass;
  final Object? useValue;
  final T? Function()? usefactory;
  final List<Type> deps;

 const Provider(
      {this.useClass, this.useValue, this.usefactory, this.deps = const []});
}

This works fine:

But when I try to directly pass-in the function. I am getting a compile error:

Any idea what is happening?

Error:

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Arguments of a constant creation must be constant expressions. (Documentation)
Try making the argument a valid constant, or use 'new' to call the constructor.

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Invalid constant value.

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The argument type 'ServiceA' can't be assigned to the parameter type 'ServiceA? Function()?'. (Documentation)

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Answer 1

Please try to remove the brackets frominject<ServiceA>(). Just make itinject<ServiceA>.

usefactory-s type is a function, but in your case, you are passingServiceAtype data.