インデクサ

https://qiita.com/ShirakawaMaru/items/7ab011afe16a743bb053

 

https://tyheeeee.hateblo.jp/entry/2014/01/25/C%23におけるIndexer詳説(ポロリもあるよ!)

 

http://dreameaters5239.hatenablog.com/entry/2017/09/23/225131

 

https://docs.microsoft.com/ja-jp/dotnet/csharp/programming-guide/indexers/indexers-in-interfaces