There's efficiency in execution time, efficiency in memory usage, efficiency in programmer time, etc. Generally programmer time is the most important thing to optimize for,
IMO, it's actually very, very rare if there's a situation where you can pinpoint "the most important thing to optimize for".

In fact, I cannot think of any.

Generally, they are all important, and it takes a good programmer/manager/project leader to strike the right balance.

In reply to Re^2: Regex Optimization Question by JavaFan
in thread Regex Optimization Question by gawatkins

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