RFC: Add enumerated extension

[lukepighetti]

I have found this extension to be useful, it allows someone to skip the common for loop pattern for accessing elements. It also supersedes the need for specialized methods like mapIndexed, whereIndexed, (I count 14 in this package). BUT the value seems low because technically we have asMap and these specialized methods already

Before

for(var i = 0; i < foo.length; i++){
  print(i);
  print(foo[i]);
}

foo.forEach((value){
  final index = foo.indexOf(value);
  print(index);
  print(value);
}

After

for(final element in foo.enumerated){
  print(element.index);
  print(element.value);
}

foo.enumerated.forEach((element){
  print(element.index);
  print(element.value);
}

Related issues

Lots of JavaScript developers rely on their overloadable map method which allows optionally accessing the index, so tutorials like this are created to shim this missing functionality https://fireship.io/snippets/dart-how-to-get-the-index-on-array-loop-map/

This is a common question on Stack Overflow

Entire videos on YouTube are dedicated to helping people with this

https://www.youtube.com/watch?v=HLMzibT2Wms

There are some related issues here, although admittedly they are closed

dart-lang/sdk#49589
dart-lang/sdk#33965

[natebosch]

We're considering making MapEntry an inline class over a Record

I wonder if we'd prefer this also be a Record, and if so, if it would be worth waiting for that language feature to publish this API.

cc @lrhn

[lukepighetti]

I had this same thought, seems like a perfect use case for a Record, and waiting for that to land would make sense to me. What would be the best way for me to know when that language feature will be available for use in this PR?

[lukepighetti]

Another option is to add this to the Iterable class in dart-lang/sdk (sdk/lib/core/iterable.dart), but I opened it up here because I figured it would be an easier conversation

[lrhn]

I'd definitely wait for Dart 3.0 and records and then add (maybe even to the platform libraries):

extension IterableIndexed<T> on Iterable<T> {
  Iterable<(int, T)> get indexed sync* { 
    var index = 0;
    for (var value in this) yield (index++, value);
  }
}

(I've already written it into the platform libraries in one of by branches. No promises that it'll land.)

[mosuem]

Closing this as it is stale. Feel free to reopen in case you still want to land it!