the two hard things

programming

The joke that there are only two hard problems in computer science: cache invalidation, naming things, and off-by-one errors.

Attributed to Phil Karlton, the line is funny because it commits an off-by-one error while listing them. Underneath the joke are three genuinely hard things: knowing when cached data is stale, choosing names that stay clear as code grows, and getting boundaries exactly right.

Also known as: two hard problems, cache invalidation and naming things, phil karlton

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