Swift was designed to have very good Objective-C and C compatibility, using the clang compiler to understand headers and generate any Swift binding/bridge at co

Swift was designed to have very good Objective-C and C compatibility, using the clang compiler to understand headers and generate any Swift binding/bridge at compile time. It will punt on trying to support some things, such as inline functions which are declared as C macros, but generally will try to expose everything. Typically a maintained Objective-C library will evaluate their ability to be used from Swift, and use attributes/macros where necessary to tweak the code import to generate a higher quality Swift interface. Examples would be declaring that a method never returns a nil value, or creating a clearer function name, or switching to the newer Objective-C enum/set styles to have the enumerations generated as Swift types rather than having their API take a raw integer constant or string. AFAIK, all of apple's frameworks are C or Objective C interfaces, and the swift interface is nearly all generated based on the code and public annotations.