Destructuring of records doesn't work in lambda parameters

[lukehutch]

This works:

List<(int, int)> vals = [];
for (var (a, b) in vals) {
  print(a+b);
}

but this fails with error The argument type 'InvalidType Function(dynamic Function(int, int))' can't be assigned to the parameter type 'dynamic Function((int, int))':

List<(int, int)> vals = [];
final sums = vals.map(((int a, int b)) => a + b).toList();  // Error

I assumed destructuring should work in lambda parameters.

Actually it doesn't work even in function definitions -- this fails with a very strange syntax error, Use the generic function type syntax to declare the parameter ''. Try using the generic function type syntax.

void sum((int a, int b)) => a + b;  // Error

The following works (by not using destructuring at all). You can't use v.a or v.b, since the field names are ignored in the type:

void sum((int a, int b) v) => v.$1 + v.$2;

[mraleph]

Duplicate of dart-lang/language#3001

(On which you have already commented few weeks ago by the way. So no need to file new issues).

[lukehutch]

Face-palm :-D Thanks for pointing that out, I totally forgot that I found that issue. I went looking for it again, and didn't find it this time...

Before I go file another dup, is there an issue for allowing v.a and v.b to be used instead of v.$1 and v.$2, in the last example I gave?

[mraleph]

is there an issue for allowing v.a and v.b to be used instead of v.$1 and v.$2, in the last example I gave?

I don't think so. Please file it at dart-lang/language repo (that's the place for all language feature requests).

The choice of names not having any meaning was deliberate, but I don't see any reason why it would not work to just allow this in a statically typed context (i.e. ignoring dynamic invocations entirely).