Swift5.1學(xué)習(xí)隨筆之指針

Swift中也有專門的指針類型，這些都被定義為Unsafe（不安全的），常見的有以下4種類型

UnsafePointer<Pointee>類似于const Pointee *
UnsafeMutablePointer<Pointee>類似于Pointee *
UnsafeRawPointer類似于const void *
UnsafeMutableRawPointer類似于void *

func test1(_ ptr: UnsafePointer<Int>) {
    print("test1", ptr.pointee)
}
func test2(_ ptr: UnsafeMutablePointer<Int>) {
    ptr.pointee = 20
    print("test2", ptr.pointee)
}

var age = 10
test1(&age) // test1 10
test2(&age) // test2 20

func test3(_ ptr: UnsafeRawPointer) {
    print("test3", ptr.load(as: Int.self))
}
func test4(_ ptr: UnsafeMutableRawPointer) {
    ptr.storeBytes(of: 30, as: Int.self)
}

var num = 10
test3(&num) //test3 10
test4(&num)
print(num) // 30

指針的使用例子??

定義一個(gè)OC的數(shù)組，利用提供的enumerateObjects進(jìn)行遍歷。block里面的三個(gè)參數(shù)，第一個(gè)代表元素劳闹、第二個(gè)是索引，第三個(gè)就是指針了洽瞬，這第三個(gè)指針就是OC中的BOOL *stop本涕，因此在swift中的寫法就是：

var arr = NSArray(objects: 11, 22, 33, 44)
arr.enumerateObjects { (<#Any#>, <#Int#>, <#UnsafeMutablePointer<ObjCBool>#>) in
    
}

arr.enumerateObjects { (element, index, stop) in
    print(index,element)
    if index == 2 {
        stop.pointee = true //等同于OC中 *stop = YES
    }
}

獲得某個(gè)變量的指針

var age = 10

var ptr = withUnsafePointer(to: &age) { $0 }
print(ptr.pointee) // 10

var ptr2 = withUnsafeMutablePointer(to: &age) { $0 }
ptr2.pointee = 30
print(age) // 30

var ptr3 = withUnsafePointer(to: &age) { (p) -> UnsafePointer<Int> in
    return p
}
print(ptr3.pointee) // 30

var ptr4 = withUnsafeMutablePointer(to: &age) { (p) -> UnsafeMutablePointer<Int> in
    return p
}
ptr4.pointee = 50
print(age) // 50

var ptr5 = withUnsafePointer(to: &age) { UnsafeRawPointer($0) }
print(ptr5.load(as: Int.self)) // 50

var ptr6 = withUnsafeMutablePointer(to: &age) { UnsafeMutableRawPointer($0) }
ptr6.storeBytes(of: 100, as: Int.self)
print(age) // 100

獲得指向堆空間實(shí)例的指針

class Person {}

var person = Person()

var ptr = withUnsafePointer(to: &person) { UnsafeRawPointer($0) }
var address = ptr.load(as: UInt.self) // person 地址值
var ptr2 = UnsafeMutableRawPointer(bitPattern: address) // 指向堆空間的地址值
print(ptr2!) // 0x0000000100669c10

print(Mems.ptr(ofRef: person)) // 0x0000000100669c10

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