2016-12-02 3:55 GMT+03:00 Ramiro Feria Purón <ramiro.feria.pu...@gmail.com>:
> *Unlike C++'s templates, a Swift's generic function is semantically a > single function.* > > Anton, could you provide further insight on this? > Basically, generic functions in Swift are implemented as functions taking an additional parameter -- witness table, which contains implementation of all functions in the protocol. For example, the following: func f<T: P>(a: T, b: T) Turns into something like: func f(a: Any, b: Any, witnessTableForT: UnsafePointer<_WitnessTable>) Returning to my cited phrase, Swift specializes generic types (with duplicated metadata; think C++ class specialization), but implements generic functions without using specialization. One can say that a generic type in Swift becomes a collection of distinct types, but a generic function remains a single function. So we can't view them equally, and current situation, where we can "explicitly specialize" types, but not functions, is not an inconsistency. I used word "semantically", because compiler can apply *specialization optimization* to a function, which is usually followed by inlining. But this optimization is guaranteed not to break the above assumptions.
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