  In this paper, we will employ the technique used in the proof of classical
Singleton bound to derive upper bounds for rank metric codes and Ferrers
diagram rank metric codes. These upper bounds yield the rank distance Singleton
bound and an upper bound presented by Etzion and Silberstein respectively. Also
we introduce generalized Ferrers diagram rank metric code which is a Ferrers
diagram rank metric code where the underlying rank metric code is not
necessarily linear. A new Singleton bound for generalized Ferrers diagram rank
metric code is obtained using our technique.
