Equivalent to Javascript yield* in C# that delegates to another iterator?

Question

Javascript has a yield* that is used to delegate to another generator or iterable object, such that the following use case produce 1 2 3 4 5 6 7 8 9:

for (const n of func1(2, 5, 8)) console.log(n)

function* func1(...nrs) {
    for (const n of nrs) {
        yield* func2(n)
    }
}

function* func2(nr) {
    yield nr - 1
    yield nr
    yield nr + 1
}

Question: Is there already, or any plan to provide an equivalent feature to yield* in C#?

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The only way that I figure out to do something equivalent in C# requires two loops in func1 such as:

static void Main(string[] args)
{
    foreach(var n in func1(2, 5, 8)) Console.WriteLine(n);
}

static IEnumerable<int> func1(params int [] nrs) {
    foreach (var iter in nrs)
        foreach (var n in func2(iter))
            yield return n;
}
static IEnumerable<int> func2(int nr) {
    yield return nr - 1;
    yield return nr;
    yield return nr + 1;
}

Answer 1

Whilst there is no equivalent to yield*, you could achieve the same in your example using Enumerable.SelectMany:

static IEnumerable<int> func1(params int[] nrs)
    => nrs.SelectMany(func2);

SelectMany also has deferred execution, as with yield.

Unfortunately, you couldn't combine this with another yield statement; you would need a foreach in that case:

static IEnumerable<int> func1(params int[] nrs)
{
    yield return 0; // Another yield
    foreach (var n in nrs.SelectMany(func2)) yield return n; // Loop now needed
}