Add shorthand for null-aware method execution

[enloc-port]

Say a class had a nullable method, i.e. an optional callback.

class Foo {
  Foo([this.doSomething]);
  final int Function() doSomething;
}

In order to avoid an error, I have to do a null-check on the method before executing it:

void main() {
  Foo foo = Foo();
  if (foo.doSomething != null) {
    foo.doSomething();
  }
}

But it would make the code look a lot cleaner, if this were possible:

void main() {
  Foo().doSomething?(); // null-aware execution
}

[eernstg]

The syntax for that feature is as follows:

class Foo {
  Foo([this.doSomething]);
  final int Function()? doSomething;
}

void main() {
  Foo().doSomething?.call(); // null-aware execution
}

We did discuss allowing f?(args) as a way to invoke f on arguments args if f is non-null and otherwise skip. But f?.call(args) does exactly that already, so the need isn't that urgent, and it may create some grammar ambiguities so it wasn't considered worthwhile.

[enloc-port]

I see. Well, f?(args) would be sweet, but I guess I could live with f?.call(args).

[eernstg]

Thanks! I think we should close this issue because the code is working as intended. Please create a new issue as needed, for instance, if you wish to make it a language proposal (in the language repository). Most likely, it could be a comment on dart-lang/language#404.