https://learn.microsoft.com/ja-jp/dotnet/api/system.collections.generic.dictionary-2.keycollection.enumerator?view=netframework-4.8.1&viewFallbackFrom=net-10.0
DictionaryTKey,TValue.KeyCollection.Enumerator Struct (System.Collections.Generic) | Microsoft...
system collectionstvalueenumeratorstructgeneric