Swift5.1学习随笔之指针

Swift中也有专门的指针类型，这些都被定义为Unsafe（不安全的），常见的有以下4种类型

1. UnsafePointer<Pointee>类似于const Pointee *
2. UnsafeMutablePointer<Pointee>类似于Pointee *
3. UnsafeRawPointer类似于const void *
4. UnsafeMutableRawPointer类似于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

---

指针的使用例子🌰

定义一个OC的数组，利用提供的enumerateObjects进行遍历。block里面的三个参数，第一个代表元素、第二个是索引，第三个就是指针了，这第三个指针就是OC中的BOOL *stop，因此在swift中的写法就是：

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
    }
}

---

获得某个变量的指针

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

---

获得指向堆空间实例的指针

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) // 指向堆空间的地址值
print(ptr2!) // 0x0000000100669c10

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