Swift 4 is now officially released! Swift 4 builds on the strengths of Swift 3, delivering greater robustness and stability, providing source code compatibility with Swift 3, making improvements to the standard library, and adding features like archival and serialization.
The Swift type-checker remains a performance bottleneck for compile times, though it has improved tremendously over the past two years. You could even say the type-checker has gone from being drunk to sober.
