"Poor-man's Span"

readonly ref struct IntSpanAggregateHelper {
	readonly ref readonly int _firstNumberRef;
	readonly int _length;

	public IntSpanAggregateHelper(ref int firstNumberRef, int length) {
		_firstNumberRef = ref firstNumberRef;
		_length = length;
	}

	public int Sum() {
		var result = 0;
		for (var i = 0; i < _length; ++i) {
			ref var curNumRef = ref Unsafe.Add(ref Unsafe.AsRef(_firstNumberRef), i);
			result += curNumRef; 
		}
		return result;
	}

	public double Average() => (double) Sum() / _length;
}

static void Test() {
	var intArray = new[] { 1, 2, 3, 4, 5 };
	var aggHelper = new IntSpanAggregateHelper(ref intArray[0], intArray.Length);
	Console.WriteLine($"Sum: {aggHelper.Sum()} | Average: {aggHelper.Average()}"); // Prints "Sum: 15 | Average: 3"
}