Infinum iOS Talks #1 - Swift under the hood: Method Dispatching by Vlaho Poluta
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This document discusses method dispatching in Swift. It explains that method dispatch determines which method is invoked in response to a message. In C++ and Objective-C, methods can use static or dynamic dispatch. Static dispatch is determined at compile-time, while dynamic dispatch is determined at runtime. The document also shows how Swift can generate Objective-C classes and use the runtime, with Swift classes being Objective-C classes under the hood. It demonstrates through benchmarks that Swift code can be as fast or faster than equivalent Objective-C code.
![[RECEIVER MESSAGE]
objc_msgSend(receiver, selector)](https://image.slidesharecdn.com/iostalk03methoddispatching-160501145047/85/Infinum-iOS-Talks-1-Swift-under-the-hood-Method-Dispatching-by-Vlaho-Poluta-4-320.jpg)
![receiver→vTable[2]()](https://image.slidesharecdn.com/iostalk03methoddispatching-160501145047/85/Infinum-iOS-Talks-1-Swift-under-the-hood-Method-Dispatching-by-Vlaho-Poluta-10-320.jpg)
![typedef struct objc_cache * Cache;
#define CACHE_BUCKET_NAME(B) ((B)->method_name)
#define CACHE_BUCKET_IMP(B) ((B)->method_imp)
#define CACHE_BUCKET_VALID(B) (B)
#define CACHE_HASH(sel, mask) (((uarith_t)(sel)>>2) & (mask))
struct objc_cache {
unsigned int mask; /* total = mask + 1 */
unsigned int occupied;
Method buckets[1];
};](https://image.slidesharecdn.com/iostalk03methoddispatching-160501145047/85/Infinum-iOS-Talks-1-Swift-under-the-hood-Method-Dispatching-by-Vlaho-Poluta-16-320.jpg)
Infinum iOS Talks #1 - Swift under the hood: Method Dispatching by Vlaho Poluta
- 1. Swift under the hood: Method Dispatching VLAHO POLUTA
- 3. Method dispatch is the algorithm used to decide which method should be invoked in response to a message.
- 5. STATIC DISPATCH Decided at Compile-time DYNAMIC DISPATCH Decided at Run-time
- 6. 02C++
- 7. STATIC DISPATCH class AnimalStatic { public: void eat() { std::out << “I’m eating food.”; } }
- 8. DYNAMIC DISPATCH class AnimalVirtual { public: virtual void eat() { std::out << “I’m eating generic food.”; } }
- 9. VTABLE IN C typedef struct { PTRFUN* vTablePtr; const char *x; const char *y; } Animal;
- 11. 03OBJECTIVE C
- 13. struct objc_class { struct objc_class *isa; struct objc_class *super_class; const char *name; long version; long info; long instance_size; struct objc_ivar_list *ivars; struct objc_method_list **methodLists; struct objc_cache *cache; struct objc_protocol_list *protocols; };
- 14. typedef struct objc_method *Method; struct objc_method { SEL method_name; char *method_types; IMP method_imp; };
- 16. typedef struct objc_cache * Cache; #define CACHE_BUCKET_NAME(B) ((B)->method_name) #define CACHE_BUCKET_IMP(B) ((B)->method_imp) #define CACHE_BUCKET_VALID(B) (B) #define CACHE_HASH(sel, mask) (((uarith_t)(sel)>>2) & (mask)) struct objc_cache { unsigned int mask; /* total = mask + 1 */ unsigned int occupied; Method buckets[1]; };
- 17. 04SWIFT
- 19. STATIC DISPATCH class AnimalStatic { final func eat() { print("I’m eating food.") } } final class AnimalStatic { func eat() { print("I’m eating food.") } }
- 20. Swift can generate Obj-C classes and use runtime Swift classes are Obj-C classes
- 21. NEW ROOT CLASS SwiftObject Conforms to the NSObjectProtocol
- 24. class AddNameHereClass { func addSubOne(num: Int) -> Int {/*…*/} } let addNameClass = AddNameHereClass() TEST let startTime = NSDate() addNameClass.addSubOne(test) x50000 times print( NSDate().timeIntervalSinceDate(startTime))
- 25. @objc class ObjcClass: NSObject { func addSubOne(num: Int) -> Int {/*…*/} } let objcClass = ObjcClass() 0.0056279…
- 26. @objc class ObjcClass: NSObject { func addSubOne(num: Int) -> Int {/*…*/} } let objcClass = ObjcClass() 0.0056279… class SwiftClass { func addSubOne(num: Int) -> Int {/*…*/} } let swiftClass = SwiftClass() 0.0014960…
- 27. @objc class ObjcClass: NSObject { func addSubOne(num: Int) -> Int {/*…*/} } let objcClass = ObjcClass() 0.0056279… class SwiftClass { func addSubOne(num: Int) -> Int {/*…*/} } let swiftClass = SwiftClass() 0.0014960… class FinalClass { final func addSubOne(num: Int) -> Int {/*…*/} } let finalClass = FinalClass() 0.0013079…
- 28. @objc class ObjcClass: NSObject { func addSubOne(num: Int) -> Int {/*…*/} } let objcClass = ObjcClass() 0.0056279… class SwiftClass { func addSubOne(num: Int) -> Int {/*…*/} } let swiftClass = SwiftClass() 0.0014960… class FinalClass { final func addSubOne(num: Int) -> Int {/*…*/} } let finalClass = FinalClass() 0.0013079…
- 29. 06CONCLUSION
- 30. SWIFT As fast or faster than Obj-C