To be honest I also find ... Ruby syntax illogical (not a Rubyist, coming from Python)
Triple dot are probably a source of silent bugs that are also harder to catch in code reviews. Also I think ..< better convey the meaning of mathematical exclusive range [a, b[ vs inclusive [a, b] Now regarding perf issue, iirc the <, ..<, ^, ..^, high, low that works for range/slice are all implemented via compiler magic, I use them all over the place because I suppose they are fast (as fast as doing b-1) and would be interested to understand perf diff.
