public override Bookmark <ValueTuple <K, V> >?Next() // ok { var b = _bmk.Next(); return((b == null)? null:(Bookmark <ValueTuple <K, V> >) new SDictBookmark <K, V>(b)); }
public override Bookmark <ValueTuple <K, V> >?First() { return((SBookmark <K, V> .Next(null, this) is SBookmark <K, V> b)? new SDictBookmark <K, V>(b):null); }