Allowing the instantiation of a generic type by calling a no-arg constructor

[lukehutch]

I want to be able to instantiate generic types, whenever those types have a no-arg constructor:

class Foo<T> {
  T createT() => T();
}

This seems to be the best that can be done right now:

class Foo<T> {
  final T Function() newT;
  Foo(T Function() newT);

  T createT() => newT();
}

void x() {
  final foo = Foo<Bar>(Bar.new);
  final bar = foo.createT();
}

(I'm sure this has been raised before, although I can't find an issue on this...)

[mraleph]

This is duplicate of dart-lang/language#1425 (other issues with discussions #3633, #7021, #24343, #30074).

For a long time we use to reject this feature, though I think there is some shifts in the language team which might indicate that we need to reconsider.

/cc @leafpetersen This is related to our discussions regarding behaviours tied to reified type parameters. Maybe we should reopen one of the issues to track the possibility that we might eventually implement this?

[leafpetersen]

Re-opened the referenced issue to serve as a the canonical tracking bug for the request.