1.方法調(diào)用
對于結構體中的?法都是靜態(tài)調(diào)?(直接調(diào)?)郭脂,那對于類?的 class 中的?法那?我們類中聲明的?法 是通過 V-table 來進?調(diào)度的澈歉。
1.1結構體方法調(diào)用
struct MyStruct {
func method1() {
print("method1")
}
func method2() {
print("method2")
}
}
let myStruct = MyStruct()
myStruct.method1()
我們看斷點
1.2類實例方法調(diào)用
我們定義如下類
class PWTeacher {
func method1() {
print("method1")
}
func method2() {
print("method2")
}
func method3() {
print("method3")
}
}
查看sil文件
sil_vtable PWTeacher {
#PWTeacher.method1: (PWTeacher) -> () -> () : @main.PWTeacher.method1() -> () // PWTeacher.method1()
#PWTeacher.method2: (PWTeacher) -> () -> () : @main.PWTeacher.method2() -> () // PWTeacher.method2()
#PWTeacher.method3: (PWTeacher) -> () -> () : @main.PWTeacher.method3() -> () // PWTeacher.method3()
#PWTeacher.init!allocator: (PWTeacher.Type) -> () -> PWTeacher : @main.PWTeacher.__allocating_init() -> main.PWTeacher // PWTeacher.__allocating_init()
#PWTeacher.deinit!deallocator: @main.PWTeacher.__deallocating_deinit // PWTeacher.__deallocating_deinit
}
我們創(chuàng)建實例展鸡,并調(diào)用方法,通過斷點看調(diào)用
let t = PWTeacher()
t.method1()
t.method2()
t.method3()
通過匯編調(diào)試埃难,我們可以看出在結構體調(diào)用方法時莹弊,是直接call地址,而類實例調(diào)用方法時涡尘,則是通過偏移找到方法在vtable的位置箱硕,然后再call調(diào)用。我們可以看出method1悟衩,method2剧罩,method3,在偏移時座泳,之間相差8字節(jié)惠昔。
extension的調(diào)用方式呢
extension PWTeacher {
func method4() {
print("method4")
}
}
let t = PWTeacher()
t.method4()
我們通過匯編調(diào)試,看一下
extension中的方法調(diào)用和struct中的方法調(diào)用是一樣的都是直接調(diào)用挑势。
1.3.方法關鍵字
final 關鍵字修飾方法
我們調(diào)用final修飾的方法镇防,從匯編看出是直接調(diào)用,從sil文件可以看到vtable文件沒有被final修飾的方法潮饱。
@objc修飾方法
調(diào)用還是在vtable中通過偏移找到函數(shù)指針進行調(diào)用的
在sil中我們可以看到
經(jīng)過@objc修飾的函數(shù)在sil中會生成兩個函數(shù)来氧,一個供swift調(diào)用,一個供OC調(diào)用香拉,但是供OC函數(shù)內(nèi)還是調(diào)用供的swift調(diào)用的函數(shù)啦扬。
swfit類繼承NSObject,
我們在oc中可以訪問,方法屬性如果添加@objc凫碌,oc內(nèi)也可以訪問
class PWTeacher :NSObject{
@objc var age:Int = 10
@objc func teachMethod(){
print("teachMethod")
}
}
我們可以在項目-Swift.h文件中看到
SWIFT_CLASS("_TtC10OCAndSwift9PWTeacher")
@interface PWTeacher : NSObject
@property (nonatomic) NSInteger age;
- (void)teachMethod;
- (nonnull instancetype)init OBJC_DESIGNATED_INITIALIZER;
@end
dynamic關鍵字
class PWTeacher {
dynamic func method1() {
print("method2")
}
}
let t = PWTeacher()
t.method1()
swift調(diào)用的時候扑毡,還是調(diào)用vtable方法表,
dynamic加@objc關鍵字
class PWTeacher {
@objc dynamic func method1() {
print("method2")
}
}
let t = PWTeacher()
t.method1()
我們看匯編
經(jīng)過objc dynamic修飾的盛险,方法調(diào)用objc_msgSend
dynamic加@_dynamicReplacement
class PWTeacher {
dynamic func method() {
print("method")
}
}
extension PWTeacher {
@_dynamicReplacement(for:method)
func method1() {
print("method1")
}
}
let t = PWTeacher()
t.method()
t.method1()
打印結果
method1
method1
調(diào)用method時瞄摊,實質(zhì)是調(diào)用的method1。調(diào)用method1和原先不變苦掘。
1.4.補充arm64下的匯編指令
blr ; 帶返回的跳轉(zhuǎn)指令换帜,跳轉(zhuǎn)到指令后邊跟隨寄存器中保存的地址
mov: 將某?寄存器的值復制到另?寄存器(只能?于寄存器與寄存器或者寄存器 與常量之 間傳值,不能?于內(nèi)存地址)鹤啡,如: 6 mov x1, x0 將寄存器 x0 的值復制到寄存器 x1 中
ldr: 將內(nèi)存中的值讀取到寄存器中惯驼,如: 9 ldr x0, [x1, x2] 將寄存器 x1 和寄存器 x2 相加作為地址,取該內(nèi)存 地址的值放?寄存器 x0 中
str : 將寄存器中的值寫?到內(nèi)存中揉忘,如: 12 str x0, [x0, x8] 跳座, 將寄存器 x0的值保存到內(nèi)存[x0 + x8]處
bl: 跳轉(zhuǎn)到某地址
2.指針
原始指針的使用
let p = UnsafeMutableRawPointer.allocate(byteCount: 32, alignment: 8)
for i in 0..<4 {
p.advanced(by: i*8).storeBytes(of: i+1, as: Int.self)
}
for i in 0..<4 {
let value = p.load(fromByteOffset: i*8, as: Int.self)
print(value)
}
p.deallocate()
allocate:分配32字節(jié)的內(nèi)存大小
advanced:代表當前p前進的步長,對于RawPointer來說泣矛,我們需要移動的是
withUnsafePointer的使用
var age = 18
age = withUnsafePointer(to: &age){
ptr in
ptr.pointee + 12
}
print(age)
能正常打印
如果我們想在內(nèi)部修改ptr的值則可以使用withUnsafeMutablePointer
var age = 18
withUnsafeMutablePointer(to: &age){
ptr in
ptr.pointee += 12
}
print(age)
打印結果是30
UnsafeMutablePointer的使用
var ptr = UnsafeMutablePointer<Int>.allocate(capacity: 1);
ptr.initialize(to: 20)
ptr.deinitialize(count: 1)
ptr.deallocate()
print(ptr.pointee)
allocate和deallocate疲眷,initialize和deinitialize是成對出現(xiàn)的
結構體指針的使用
struct PWPerson {
var age = 18
var height = 180
}
var ptr = UnsafeMutablePointer<PWPerson>.allocate(capacity: 2)
ptr.initialize(to: PWPerson())
ptr.advanced(by: 1).initialize(to: PWPerson(age: 20, height: 190))
//方法1訪問
print(ptr[0])
print(ptr[1])
//方法2訪問
print(ptr.pointee)
print((ptr+1).pointee)
//方法3訪問
print(ptr.pointee)
print(ptr.successor().pointee)
ptr.deinitialize(count: 2)
ptr.deallocate()
在advanced中因為我們知道類型所以知道一次要移動的字節(jié)數(shù),所以我們在這里寫1您朽,2狂丝,3等步數(shù),
而UnsafeMutableRawPointer移動的是字節(jié)數(shù)哗总,因為不知道步長是多少几颜。
swift實例轉(zhuǎn)化成結構體
class PWTeacher {
var age:Int = 18
}
struct HeapObject {
var kind:UnsafeRawPointer
var strongRef:UInt32
var unownedRed :UInt32
}
struct lg_swift_class {
var kind: UnsafeRawPointer
var superClass: UnsafeRawPointer
var cachedata1: UnsafeRawPointer
var cachedata2: UnsafeRawPointer
var data: UnsafeRawPointer
var flags: UInt32
var instanceAddressOffset: UInt32
var instanceSize: UInt32
var flinstanceAlignMask: UInt16
var reserved: UInt16
var classSize: UInt32
var classAddressOffset: UInt32
var description: UnsafeRawPointer
}
var t = PWTeacher()
//Unmanaged 類似于OC和CF所有權的轉(zhuǎn)換
let ptr = Unmanaged.passUnretained(t as AnyObject).toOpaque()
//ptr獲得的指針類型為UnsafeMutableRawPointer
//通過bindMemory,從RawPointer轉(zhuǎn)換成UnsafeMutablePointer讯屈,
let heapPoiner = ptr.bindMemory(to: HeapObject.self, capacity: 1)
let metaPtr = heapPoiner.pointee.kind.bindMemory(to: lg_swift_class.self, capacity: 1)
print(metaPtr.pointee)
總結:
Unmanaged.passUnretained是把一個UnsafePointer(UnsafeMutablePointer)類型的指針轉(zhuǎn)成UnsafeMutableRawPointer
ptr.bindMemory:是UnsafeMutableRawPointer指針綁定為UnsafePointer(UnsafeMutablePointer)指針蛋哭,如果ptr已經(jīng)是UnsafePointer(UnsafeMutablePointer)則重新綁定
bindMemory(to: Capacity:) : 更改內(nèi)存綁定的類型,如果之前沒有綁定涮母,那么就是?次綁定谆趾;如果綁 定過了,會被重新綁定為該類型
UnsafePointer類型的轉(zhuǎn)換 UnsafePointer<(Int,Int)>轉(zhuǎn)化成UnsafePointer<Int>
var tul = (10,12)
func test(ptr:UnsafePointer<Int>){
print(ptr.pointee)
}
withUnsafePointer(to: &tul) {
(tulPtr:UnsafePointer<(Int,Int)>) in
test(ptr: UnsafeRawPointer(tulPtr).assumingMemoryBound(to: Int.self))
}
assumingMemoryBound: 假定內(nèi)存綁定叛本,這?是告訴編譯器:哥們我就是這種類型沪蓬,你不要檢查我 了
withMemoryRebound UnsafePointer<Int>轉(zhuǎn)化成UnsafePointer<UInt64 >
var age = 10
func test(ptr:UnsafePointer<UInt64>) {
print(ptr.pointee)
}
withUnsafePointer(to: &age) { (ptr:UnsafePointer<Int>) in
test(ptr: ptr.withMemoryRebound(to: UInt64.self, capacity: 1){$0})
}