`cascade_invocations` false positives

[vsevolod19860507]

cascade_invocations false positives

void main() {
  final List<int> items = [];
  var g = 7;
  items.clear();
  items.addAll([g]); // LINT
}

[jamesderlin]

Why is this a false positive? What's wrong with:

items
  ..clear()
  ..addAll([g]);

?

[vsevolod19860507]

Why is this a false positive? What's wrong with:

items
  ..clear()
  ..addAll([g]);

?

The problem is with void!

[bwilkerson]

Could you be a little more explicit? I don't see any particular problem caused by void in this example.

[jamesderlin]

@vr19860507 If you believe there would be some problem from clear() returning void, the point of using the cascade operator (items..clear()) instead of normal member access (items.clear()) is that items..clear() evaluates to items and ignores the return value of clear().

[vsevolod19860507]

@jamesderlin @bwilkerson

Just enable "cascade_invocations". And just paste this code

void main() {
  final List<int> items = [];
  var g = 7;
  items.clear();
  items.addAll([g]); // LINT
}

into the editor.

And you will understand what I'm talking about!

[jamesderlin]

@vr19860507 The lint is telling you that you can use the cascade operator instead, as I showed in #58050. The lint seems correct; what makes you think that it is a false positive?

[bwilkerson]

Try running the following code:

void main() {
  final List<int> items = [];
  var g = 7;

  items.clear();
  items.addAll([g]);
  print(items);

  items..clear()..addAll([g]);
  print(items);
}

This will print out two identical lines because the two ways of writing the code are equivalent. In both cases any exiting contents of the list are removed (the invocation of clear) and then a single item is added to the list (the invocation of addAll).

I suspect that what wasn't clear is that the cascade operator means to invoke both clear and addAll on the result of the expression before the first cascade operator, which in this case is items.

[vsevolod19860507]

@bwilkerson @jamesderlin Checked it now, it works!

items
  ..clear()
  ..addAll([g]);

But I remember exactly that when I opened this issue it did not work... I don't know, maybe I was mistaken, or maybe they fixed it...

Thank you anyway!

[bwilkerson]

You're welcome. I'm glad it's working for you.