"Developing Games With Ruby" Stuck at creating prototype tank game

I don’t know why , i followed the code sample and it didn’t work, it seems like it is outdated?
Is there anyone who can fix this?

You may want to give us a bit more context. What guide did you follow? What are you stuck on?

I currently following “Developing Games With Ruby” Read Developing Games With Ruby | Leanpub

Im stuck at “Prototyping The Game” chapter where i tried the program which the compilation failed.