Why doesn't .map or .forEach expose an index?

[lukepighetti]

[matanlurey]

Both of these functions are actually on Iterable, and inherited through List.

It is possible to have an Iterable without a definitive length (or index, of any sort). For example, imagine a virtual-scrolling list. Of course, it is very easy to write such functionality yourself, if you'd like:

void forEachIndex<T>(Iterable<T> elements, void Function(T, int) forEach) {
  var i = 0;
  for (final element in elements) {
    forEach(element, i++);
  }
}

void example(Iterable<String> elements) {
  forEachIndex(elements, (e, i) {

  });
}

You might also find following this useful: #9991, then you'd do:

import 'package:your_package/your_package.dart';

void example(Iterable<String> elements) {
  elements.forEachIndex((el, i) { ... });
}

[alan-knight]

The asMap method probably does what you want.

  var thing = [5,4,3,2,1];
  thing.asMap().forEach((k, v) => print("$k : $v"));

0 : 5
1 : 4
2 : 3
3 : 2
4 : 1

[xqdd]

 items: [
            ["HOME", Icons.home],
            ["MESSAGE", Icons.message],
            ["READ", Icons.chrome_reader_mode],
            ["ACITIVTY", Icons.local_activity],
            ["ME", Icons.person],
          ]
              .asMap()
              .map<int, BottomNavigationBarItem>(
                  (k, v) => MapEntry(k, _genBottomBarItem(k, v[0], v[1])))
              .values
              .toList(),