Improve `typedef` Usability for Named Tuple-like Structures in Dart

[stephane-archer]

When using typedef for defining tuple-like structures, the behavior feels unintuitive and error-prone. For example, in the code below:

import 'package:flutter/material.dart';

typedef FeedbackData = (String message, Color color);

void Function(FeedbackData) getDisplayFeedbackForTheUser(
    BuildContext context) {
  return (feedbackData) {
    final snackBar = SnackBar(
      backgroundColor: feedbackData.$2,
      content: Text(feedbackData.$1),
      duration: feedbackData.$2 != Colors.green ? Duration(seconds: 6) : Duration(seconds: 4),
    );
    ScaffoldMessenger.of(context).showSnackBar(snackBar);
  };
}

The FeedbackData fields (message and color) must be accessed using . $1 and . $2. This feels strange, non-descriptive, and introduces potential errors due to lack of clarity.

Current Workaround:

I can rewrite the typedef like this:

typedef FeedbackData = ({String message, Color color});
This makes field access more intuitive:

final snackBar = SnackBar(
  backgroundColor: feedbackData.color,
  content: Text(feedbackData.message),
  duration: feedbackData.color != Colors.green ? Duration(seconds: 6) : Duration(seconds: 4),
);

However, this approach makes creation tedious because I need to explicitly name every parameter when creating a FeedbackData object.

Suggestion:

Can the following behavior be supported for typedef?

typedef FeedbackData = (String message, Color color);

void Function(FeedbackData) getDisplayFeedbackForTheUser(
    BuildContext context) {
  return (feedbackData) {
    final snackBar = SnackBar(
      backgroundColor: feedbackData.color,
      content: Text(feedbackData.message),
      duration: feedbackData.color != Colors.green ? Duration(seconds: 6) : Duration(seconds: 4),
    );
    ScaffoldMessenger.of(context).showSnackBar(snackBar);
  };
}

Here, FeedbackData would behave like a named tuple, allowing both intuitive field access (feedbackData.message and feedbackData.color) and concise creation syntax.

Why This Matters:

The current behavior of typedef makes tuple-like constructs harder to use in a way that is both expressive and practical. Enhancing typedef usability for named field access would make writing cleaner, safer, and more readable code easier.

[dart-github-bot]

Summary: Current typedef handling of tuple-like structures is unintuitive and error-prone, requiring awkward $1, $2 access. Proposed improvement: allow named field access for cleaner, safer code.

[mraleph]

Duplicate of dart-lang/language#3487

[stephane-archer]

While related, this concern a typedef and it's usage