Dart's odd problems

[seha-bot]

First off I would like to apologise because this is not an issue with invariant_collection. I am writing here only because I don't know how to contact you ':-)

Your attention to writing safe and readable code and your contribution to Dart made me reach out to you for assistance.
I am collecting examples of "odd" Dart code for my presentation.

What do I mean by "odd"?

Odd code is code which is either undefined or unclear. Undefined is self-explanatory, but I doubt there is anything undefined in the Dart standard (you tell me :D). Unclear is code which can confuse the reader and induce him to thinking it does thing X, when in reality it does thing Y.

Motivation

I am a member of a discord server focusing on embedded engineering and it features an "odd problems emporium" channel. People post odd code and without using a compiler you need to explain what that code does.

Example:

/* C99 */
int main(void) {
    int i = 1;
    return i / i++;
}

What does this program return? Solution is that this is UB as there is no sequence point.

What have I collected so far

No real type safety

dart-lang/sdk#55021

Default parameters are allowed to be overriden

class Foo {
  int bar([int? baz = 0]) {
    return baz!;
  }
}

final class Bar extends Foo {
  @override
  int bar([int? baz]) {
    return baz!;
  }
}

void main() {
  Foo foo1 = Foo();
  Foo foo2 = Bar();
  print(foo1.bar());
  print(foo2.bar());
}

the existence of covariant

Return values of methods are allowed to be specialized, while for parameters you need covariant.
I will present this as "odd" because most people will be confused after I show them these two examples in succession:

Slide 1:

abstract class Foo {
  Foo bar();
}

final class Bar extends Foo {
  @override
  Bar bar() {
    return this;
  }
}

Slide 2:

abstract class Foo {
  void baz(Foo foo);
}

final class Bar extends Foo {
  @override
  void baz(Bar bar) {}
}

void is of type Null and has a size

void main() {
  List<void> foos = <void>[];
  foos.add(print("0"));
  foos.add(null);
  for (final e in foos.cast<Null>()) {
    print(e);
  }
}

Pattern matching is falsely non-exhaustive

dart-lang/language#3633

Conditional member access operator discards the assignment operations

final class Foo {
  int i = 0;
}

void main() {
  Foo? foo;
  int i = 0;
  foo?.i = ++i;
  print(i);
}

Note

I am not trying to get anyone to dislike Dart and all of these "issues" have a valid reasoning behind their existence.
Thank you for reading this and I hope you can provide some more examples of oddity in Dart. Also, would you like to say something so I can put it as a quote in the presentation?

Cheers

[eernstg]

Hello @seha-bot, I tried to move the issue to the Dart language repository where it seems to be a much better fit, but github doesn't want to do that. Please just copy your text and create the issue there: https://github.com/dart-lang/language/issues/new?assignees=&labels=request&projects=&template=1-PROBLEM_STATEMENT.md

[seha-bot]

I've copied it over to there:
dart-lang/language#3637