SLC: IsSeq for IArray

Scala Standard Library
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As described in scala collections docs, IsSeq, IsIterable etc allow truly generic collection-style algorithms:

I would propose to provide an instance for IArray (to accompany the Array implementation), this one will be based on the immutable.ArraySeq class for widening operations (otherwise returns IArray e.g. for .filter).

Implementation here: Add an implementation of IsSeq for IArray. by bishabosha · Pull Request #24552 · scala/scala3 · GitHub

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Could you add an example of what was not possible before, but is now possible with your change? How does it help the users? It would help a lot to get a full picture here.

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taking the example from the docs, here is a function that you can define currently that will not work for IArray, but will work after the change. (it works for standard Array)

extension [Repr](repr: Repr)(using iter: IsIterable[Repr])
  def sumBy[B: Numeric](f: iter.A => B): B =
    // from https://docs.scala-lang.org/overviews/core/custom-collection-operations.html
    val coll = iter(repr)
    val it = coll.iterator
    var result = f(it.next())
    while it.hasNext do
      result = summon[Numeric[B]].plus(result, f(it.next()))
    result

case class Rational(num: Int, denom: Int):
  def toDecimal = BigDecimal(num) / denom

Seq(Rational(1,2), Rational(1,4)).sumBy(_.toDecimal) // ok
IArray(Rational(1,2), Rational(1,4)).sumBy(_.toDecimal) // error
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