Best is quite subjective. Non nullable default types, defer, patterns are great ideas. Virtual by default, associated protocols instead of generic protocol,

Best is quite subjective. Non nullable default types, defer, patterns are great ideas. Virtual by default, associated protocols instead of generic protocol, Exception handling designed based on how objc passes nserror, Generic instantiation is done at runtime, not by the compiler, so field access and even defining locals involves needless math, All things with a lot better alternatives at the time swift was designed.