Try some JSON benchmarks with Codables in Swift vs serde in Rust. Rust smokes Swift, something like 20x.
Incidentally I've spent considerable effort on this problem, including writing a prototype faster JSON parser in Swift (still about 3x slower than Rust, but a huge speedup over what's there). I couldn't get anyone in the Swift community to care enough to motivate me to finish the work, which is indicative of a deeper problem: Swift just doesn't have "performance culture," the benchmark game results notwithstanding.
Incidentally I've spent considerable effort on this problem, including writing a prototype faster JSON parser in Swift (still about 3x slower than Rust, but a huge speedup over what's there). I couldn't get anyone in the Swift community to care enough to motivate me to finish the work, which is indicative of a deeper problem: Swift just doesn't have "performance culture," the benchmark game results notwithstanding.