References

You can now return values by reference from a method as well as consume them. This is a little like working with pointers in C but safer. For example, you can only return references that were passed to the method, and you can't modify references to point to a different location in memory. This is a very specialist feature, but in certain niche situations, it can dramatically improve performance.

Consider the following method:

private static ref string GetFirstRef(ref string[] texts)
{
    if (texts?.Length > 0)
    {
        return ref texts[0];
    }
    throw new ArgumentOutOfRangeException();
}

You could call this method like so, and the second console output line would appear differently (one instead of 1):

var strings = new string[] { "1", "2" };
ref var first = ref GetFirstRef(ref strings);
Console.WriteLine($"{strings?[0]}"); // 1
first = "one";
Console.WriteLine($"{strings?[0]}"); // one