#592 – Optional Parameters in Indexers

In addition to defining optional parameters within methods, you can also include an optional parameter in an indexer.

For example, assume that we have a Dog class that keeps track of the sounds that a dog makes when he barks and that we’ve defined an indexer for the class that retrieves a “bark sound” from that list.

        public string this[int i]
        {
            get
            {
                return BarkRecord[i];
            }
        }

Using the indexer:

            kirby.Bark("Woof");
            kirby.Bark("Bow-wow");
            kirby.Bark("Urgh");

            Console.WriteLine(kirby[2]);

We can now add an optional parameter to the indexer, to indicate that we’d like the date/time of the bark returned as well.

        public string this[int i, bool includeTime = false]
        {
            get
            {
                string barkInfo = BarkRecord[i];

                if (includeTime)
                    barkInfo = barkInfo + string.Format(" at {0}", BarkTime[i]);

                return barkInfo;
            }
        }

Using the indexer:

            Console.WriteLine("Bark at [2]={0}", kirby[2]);
            Console.WriteLine("Bark at [1]={0}", kirby[1, true]);