tracking: support iterables in @std/collections APIs

[iuioiua]

Following on from #4671, it seems there are APIs within @std/collections that could support Iterables rather than just arrays. From a quick scan, these symbols might be able to be tweaked to support iterables:

• chunk()
• dropLastWhile()
• dropWhile()
• intersect()
• sample()
• slidingWindows()
• sortBy()
• takeLastWhile()
• takeWhile()
• withoutAll()

See #3390 for an example of how with was done for groupBy().

[Liam-Tait]

A larger change to consider. Should collections use generators? This would be breaking change.

Generators give lazy evaluation, memory efficiency, and sometimes better performance

Example:

function* takeWhile<T>(
  iterable: Iterable<T>,
  predicate: (el: T) => boolean,
): Generator<T> {
  for (const element of iterable) {
    console.log(`takeWhile(): ${element}`);
    if (!predicate(element)) {
      break;
    }
    yield element;
  }
}

function* map<T, U>(
  iterable: Iterable<T>,
  transform: (el: T) => U,
): Generator<U> {
  for (const element of iterable) {
    console.log(`map(): ${element}`);
    yield transform(element);
  }
}

const arr = [1, 2, 3, 4, 5, 6, 7, 8, 9];
const result = takeWhile(map(arr, (n) => n * 100), n => n < 500)
console.log([...result])

[iuioiua]

I think we should stick to the current approach unless the performance benefits are sufficient. We'd have to measurements before coming to that decision.

[Liam-Tait]

The move to iterables means that generators that never return are valid arguments.

  function* counter() {
    let i = 0;
    while (true) {
      yield i++;
    }
  }

Many of these functions would hang

Examples:

takeWhile(counter(), v === 0) // predicate will never be true
chunk(counter(), 10)
dropLastWhile(counter, v => v > 30)
dropWhile(counter, v => v === 0) // predicate will never be true

Here are some options:

1. Don't handle the case, onus is on the user to know the generator is infinite. Likely case is throwing an Uncaught RangeError: Invalid array length when the result array is too long
2. Catch the error and rethrow?
3. Have a max iterations option available