collection literals C#

program.cs

// Gives an array of 3 elements
IEnumerable<ulong>  x0 = Enumerable.Concat<ulong>([1], Unbounded());
ulong[]             y0 = x0.Take(3).ToArray();

// Crashes with out of memory after some time
IEnumerable<ulong>  x1 = [1, ..Unbounded()];
ulong[]             y1 = x0.Take(3).ToArray();

IEnumerable<ulong> Unbounded()
{
    ulong i = 0;
    while(true)
    {
        ++i;
        Console.WriteLine($"Generated: {i}");
        yield return i;
    }
}