public IEnumerable <IFile> GetFiles() => ChildFileSystemItems.OfType <IFile>();
public IEnumerable <IDirectory> GetSubdirectories() => ChildFileSystemItems.OfType <IDirectory>();
public IEnumerable <IFile> GetFiles() => ChildFileSystemItems.OfType <IFile>();
public IEnumerable <IDirectory> GetSubdirectories() => ChildFileSystemItems.OfType <IDirectory>();