一.swift指针类型

swift认为指针是不安全的，所有指针的类的前缀为unsafe

• UnsafePointer : 指定类型的指针，指针不可变, 相当于const Type *
• UnsafeMutablePointer : 限定类型的指针，可变指针，相当于 Type *
• UnsafeRawPointer: 不限定类型, 可以指向任何类型，但是不可变, 相当于 const void *
• UnsafeMutableRawPointer: 指向任意类型，而且可变，相当于void *

swift	c
UnsafePointer	const Type *
UnsafeMutablePointer	Type *
UnsafeRawPointer	const void *
UnsafeMutableRawPointer	void *

二.swift指针内存管理

源码demo

///     let bytesPointer = UnsafeMutableRawPointer.allocate(byteCount: 4, alignment: 1)
///     bytesPointer.storeBytes(of: 0xFFFF_FFFF, as: UInt32.self)
///
///     // Load a value from the memory referenced by 'bytesPointer'
///     let x = bytesPointer.load(as: UInt8.self)       // 255
///
///     // Load a value from the last two allocated bytes
///     let offsetPointer = bytesPointer + 2
///     let y = offsetPointer.load(as: UInt16.self)     // 65535

自己操作指针，在allocate后要进行deallocate释放该指针

---

三.withUnsafeMutablePointer的使用

var i = 11

let p0 = withUnsafeMutablePointer(to: &i, {$0})
print(p0.pointee)//11

//不简写的状态
let p1 = withUnsafeMutablePointer(to: &i) { ptr in
    return ptr
}
print(p1.pointee)//11

//@inlinable public func withUnsafeMutablePointer<T, Result>(to value: inout T, _ body: (UnsafeMutablePointer<T>) throws -> Result) rethrows -> Result
//可以返回其他值,因为Result的值是由闭包的Result决定的
let p2 = withUnsafePointer(to: &i) { ptr in
    ptr.pointee + 10
}
print(p2)//21 此时的p2就是一个Int值,而不是指针

四.Unmanaged

class Cls {
}
var c = Cls()
let ptr = Unmanaged.passUnretained(c as AnyObject).toOpaque()
print(ptr)//0x00006000026c40c0

• 注意：Unmanaged和withUnsafeMutablePointer获取到的地址不一样，需要研究下
• 使用bindMemory可以修改类型