Added Iterable<Comparable> Extensions: .min and .max

[ChristianKleineidam]

As discussed in #41902 I created two extensions to Iterable. .min that returns the smallest element and .max return s the largest one.

When it comes to the question of what to do when multiple elements have the same value I orientied myself with Pythons implementation of min() and max() that returns that both return the first value.

I copied the headers from other files in their respective folders.

[parlough]

For reference the CL for this is here: https://dart-review.googlesource.com/c/sdk/+/148744

[lrhn]

This is not a bad idea. I'd like to consider implications a little more before landing our first extension methods in the platform libraries.

For example, should it be a method instead of a getter? Then we can do:

extension IterableExtension<T> on Iterable<T> {
  T max(int compare(T a, T b)) { 
    var it = this.iterator;
    if (!it.moveNext()) throw StateError("no element");
    var max = it.current;
    while (it.moveNext()) {
      var next = it.current;
      if (max.compareTo(next) < 0) max = next;
    }
    return max;
  }
}
extension IterableComparableExtension<T extends Comparable<T>> on Iterable<T> {
  T max([int compare(T a, T b)]) => 
      IterableExtension(this).max(compare ?? (a, b) => a. compareTo(b));
}

That would be a more general API, and would still allow you to get the maximum of comparables without providing a comparator.

(I think we might indeed want that, and I'm currently working on something similar aimed for package:collection).

[ChristianKleineidam]

To me it appears as if the max() you define on the general Iterable doublicates the functionality of the existing .reduce()-method and as such provides no additional value.

[lrhn]

It's not exactly the same as reduce.

If you have

T Function(T, T) maxBy<T>(int compare(T a, T b)) => (T a, T b) => compare(a, b) < 0 ? b : a;

then you can indeed do values.max(compare) as values.reduce(maxBy(compare)). It's still more convenient to have it directly, which is why this is a extension method rather than a method on Iterable itself.

I have no problem having more than one way to do a thing, as long as the more specialized one is often useful and more readable.

[ChristianKleineidam]

You are right that gives additional value. Given that sort() also takes such a compare function, it would also reuse existing patterns to do it that way.

Having a function would also mean that you can pass a default value for cases where the Iterator is empty like Pythons max and min functions have.

[PiN73]

Using method instead of getter might make sense because it's O(N)

[mit-mit]

Closing as assumed stale