pointers.cs

    static void Main(string[] args)
    {
        var vec = new Vector3 {X = 10, Y = 20, Z = 30};
        Foo(ref vec);
    }

    public static unsafe void Foo(ref Vector3 vec)
    {
        fixed (Vector3* ptr = &vec)
        {
            Console.WriteLine($"{ptr->X += 10}, {ptr->Y += 10}, {ptr->Z += 10}");
        }
    }

    public ref struct Vector3
    {
        public float X;
        public float Y;
        public float Z;
    }