System.Collections.ArrayList.SyncIList.this C# (CSharp) Method

            public virtual Object this[int index]
            {
                get
                {
                    lock (_root)
                    {
                        return _list[index];
                    }
                }
                set
                {
                    lock (_root)
                    {
                        _list[index] = value;
                    }
                }
            }