Avoiding Hash Lookups in a Ruby Implementation, on the quest to eliminate the use of ad-hoc hashes inside JRuby. I love that the cardinal sin of a runtime is to avoid memory reads. It makes avoiding random database lookups in web applications look like a walk in the park.
On the other hand, consider how much fun it is to write compilers; their cardinal sin is to avoid conditionals or anything that would stall the processor pipeline. If that seems pedestrian, then consider the cardinal sin of a processor designer: don’t do anything that will take longer than one clock cycle, or half a billionth of a second if you’re keeping score at home.