In Dart, we merged tuples and records into a single construct. A record can have positional fields, named fields, or both. A record type can appear anywhere a type annotation is allowed. So in Dart these are both fine:

    (int, int) can() => (1, 2);
    ({int sum, int product}) alsoCan() => (sum: 1, product: 2);
    (int, {int remainder}) evenThis() => (1, remainder: 2);

The curly braces in the record type annotation distinguish the named fields from the positional ones. I don't love the syntax, but it's consistent with function parameter lists where the curly braces delimit the named parameters.

https://dart.dev/language/records