return as an expression

[mattrberry]

The motivation for this is that I'd love to be able to return from a switch expression. i.e.:

String? someFunc(Node node) {
  final err = switch(node) {
    case Foo(field: String toReturn) => return toReturn,
    _ => 'some error message',
  };
  handleErr(err);
  return null;
}

Since return introduces a statement rather than expression, this isn't possible. I see in the language spec that that throw is an expression, making switch(x) { _ => throw 'foo' } legal. Is there a motivation for supporting throw and not other control flow keywords? In particular, I'm thinking return, yield, continue, break, and rethrow. Maybe it'd be easy to redefine these as expressions, which would be backwards compatible given that Dart already has an expression statement.

For a relatively mainstream language that has pattern matching and treats continue, break, and return as expressions, we can look at Rust's expression grammar.

(One other thing I'll point out with the introduction of switch expressions is that I'd love to run arbitrary groups of statements in an expression; something like #132)

[eernstg]

I'll close this issue as a duplicate of #2025.

@mattrberry, you might want to vote for #2025 and/or comment on it. Otherwise, you could create a new issue that puts more emphasis on why this is different from #2025.

[mattrberry]

Looks like #2025 covers my request. Thanks for deduping!

(I'm not happy with GitHub's issue search. I clicked through a few pages of searches for duplicates before posting.. :/ )