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Showing posts from October, 2015

This One Subtle Bug You Might Not See Coming

Sometimes bugs are obvious. You used a ++ where you should have used a --. Other times, bugs are much less obvious. A regular expression was missing an escape of a .. Then there are those bugs that are so subtle and insidious that they deserve their own blog post just to document and excoriate them. This post is about one of those bugs.

Fortunately for me, this wasn't my bug. It was a bug hidden in a Programmers.SE question. The questioner was blaming himself for not seeing or understanding a change in an external library, and he was desperately looking for a way to write better code to account for such changes in the external library. What did that library do? There was a method that returned a long, where the long was milliseconds since epoch. In the update, the method was changed so that it still returned a long, but the long now represented nanoseconds since epoch.

Putting aside the discussion about whether a long has enough precision, this change is a special type of awful. T…