Can I quick get table last key value use like at(idx) function?

[Angluca]

I write func print unicode font must O(1) speed, unicode cjk have 0 ~ 195103, 
Of cource haven't all char It's to large( So only have 18000+ zh, jp ,kr .. 
fonts: table[Rune, Rect(x,y,w,h)] get pixel fonts on png) I think use hash 
table is best way maybe... Is there have better type structure to use in nim ?