Infinum iOS Talks #1 - Swift under the hood: Method Dispatching by Vlaho Poluta

Swift under the hood:
Method Dispatching
VLAHO POLUTA

Method dispatch is the algorithm used to
decide which method should be invoked in
response to a message.

[RECEIVER MESSAGE]
objc_msgSend(receiver, selector)

STATIC DISPATCH
Decided at Compile-time
DYNAMIC DISPATCH
Decided at Run-time

STATIC DISPATCH
class AnimalStatic
{
public:
void eat() { std::out << “I’m eating food.”; }
}

DYNAMIC DISPATCH
class AnimalVirtual
{
public:
virtual void eat() { std::out << “I’m eating generic food.”; }
}

VTABLE IN C
typedef struct {
PTRFUN* vTablePtr;
const char *x;
const char *y;
} Animal;

objc_msgSend(receiver, selector)

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;
};

typedef struct objc_method *Method;
struct objc_method {
SEL method_name;
char *method_types;
IMP method_imp;
};

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];
};

STATIC DISPATCH
class AnimalStatic {
final func eat() {
print("I’m eating food.")
}
}
final class AnimalStatic {
func eat() {
print("I’m eating food.")
}
}

Swift can generate Obj-C classes and
use runtime
Swift classes are Obj-C classes

NEW ROOT CLASS
SwiftObject
Conforms to the NSObjectProtocol

class AddNameHereClass {
func addSubOne(num: Int) -> Int {/*…*/}
}
let addNameClass = AddNameHereClass()
TEST
let startTime = NSDate()
addNameClass.addSubOne(test) x50000 times
print( NSDate().timeIntervalSinceDate(startTime))

@objc class ObjcClass: NSObject {
}
let objcClass = ObjcClass()
0.0056279…

}
0.0056279…
class SwiftClass {
}
let swiftClass = SwiftClass()
0.0014960…

}
0.0056279…
class SwiftClass {
}
let swiftClass = SwiftClass()
0.0014960…
class FinalClass {
final func addSubOne(num: Int) -> Int {/*…*/}
}
let finalClass = FinalClass()
0.0013079…

SWIFT
As fast or faster than Obj-C

Infinum iOS Talks #1 - Swift under the hood: Method Dispatching by Vlaho Poluta

Infinum iOS Talks #1 - Swift under the hood: Method Dispatching by Vlaho Poluta

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Infinum iOS Talks #1 - Swift under the hood: Method Dispatching by Vlaho Poluta