Writing Swift, while living on Objective-C
summary
Yelp describes why a large Objective‑C app (launched 2008, handling 92M monthly mobile uniques and 108M reviews) moves to Swift incrementally: add an autogenerating bridging header, annotate headers with nullability annotations and use Objective‑C generics to turn IUOs and [Any] into safe Swift optionals and typed collections. Migration hits concrete costs: ~900 Swift files cause full builds to rise to ~7 minutes until autogeneration is replaced and headers drop to ~300, and some APIs need signature changes (completion closures) to avoid lost information.
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