swift Class的内存布局

class Human {

    //8 type or isa

    //retainCount

    var age: Int?//16

    var name: String?//16

    var nicknames: [String] = [String]()

    

    //返回指向 Human 实例头部的指针

    func headPointerOfClass() -> UnsafeMutablePointer<Int8> {

        let opaquePointer = Unmanaged.passUnretained(self as AnyObject).toOpaque()

        let mutableTypedPointer = opaquePointer.bindMemory(to: Int8.self, capacity: MemoryLayout<Human>.stride)

        return UnsafeMutablePointer<Int8>(mutableTypedPointer)

    }

}

MemoryLayout<Human>.size       //8

let human = Human()

let arrFormJson = ["goudan","zhaosi", "wangwu"]

//拿到指向 human 堆内存的 void * 指针

let humanRawPtr = UnsafeMutableRawPointer(human.headPointerOfClass())

//nicknames 数组在内存中偏移 48byte 的位置(8+8+16+16)

let humanNickNamesPtr =  humanRawPtr.advanced(by: 48).assumingMemoryBound(to: Array<String>.self)

print(human.nicknames)

//[]

humanNickNamesPtr.initialize(to: arrFormJson)

print(human.nicknames)

human.nicknames           //["goudan","zhaosi", "wangwu"]

let retainCount =  humanRawPtr.advanced(by: 8).assumingMemoryBound(to: Int8.self)

print(retainCount.pointee)