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Swift知识

Swift使用enum抹平数组元素差异实例详解

swift内存管理指针类型使用实例详解

swift指针及内存管理内存绑定实例详解

swift API 绑定

swift提供了3种不同的API来绑定/重新绑定指针

assumingMemoryBound(to:)
bindMemory(to: capacity:)
withMemoryRebound(to: capacity: body:)

绕过编译器检查 - assumingMemoryBound

就是假定内存绑定

func testPointer(_ p: UnsafePointer<Int>) {
  print(p)
}
let tuple = (30, 40)
withUnsafePointer(to: tuple) { (tuplePtr: UnsafePointer<(Int, Int)>) in
  testPointer(UnsafeRawPointer(tuplePtr)
  .assumingMemoryBound(to: Int.self))
}

其实两者本质没什么区别，都是指向内存的指针

UnsafePointer 指向1块Int内存

UnsafePointer<Int, Int> 指向一个元组tuple内存, 也就是一块连续的内存，包含连个连续的Int

两者都是首地址

一种方式就是不强转 UnsafePointer<Int, Int> 为 UnsafePointer

先把元组指针转换成原始指针 UnsafeRawPointer(tuplePtr)
原始指针调用 assumingMemoryBound 绑定成Int 指针 UnsafeRawPointer(tuplePtr).assumingMemoryBound(to: Int.self)

func testPointer(_ p: UnsafePointer<Int>) {
  print(p[0])
  print(p[1])
}
let tuple = (30, 40)
withUnsafePointer(to: tuple) { (tuplePtr: UnsafePointer<(Int, Int)>) in
  testPointer(UnsafeRawPointer(tuplePtr).assumingMemoryBound(to: Int.self))
}

结果

30

40

assumingMemoryBound的意义在于：

有时候不想做指针类型转换来增加代码的复杂度

就可以调用此api绕过编译器检查，但是并没有发生实际的指针转换

内存转换 - bindMemory

实际发生了转换，改变当前内存指针绑定的类型

func testPointer(_ p: UnsafePointer<Int>) {
  print(p[0])
  print(p[1])
}
let tuple = (30, 40)
withUnsafePointer(to: tuple) { (tuplePtr: UnsafePointer<(Int, Int)>) in
  testPointer(UnsafeRawPointer(tuplePtr)
  .bindMemory(to: Int.self, capacity: 1))
}

结果

30

40

bindMemory - 相比于assumingMemoryBound，就是改变内存绑定类型

临时改变内存绑定 - withMemoryRebound

func testPointer(_ p: UnsafePointer<Int8>) {
  print(p)
}
let UInt8Ptr = UnsafePointer<UInt8>.init(bitPattern: 30)
UInt8Ptr?.withMemoryRebound(to: Int8.self, capacity: 1, 
	{ (Int8Ptr: UnsafePointer<Int8>) in
  testPointer(Int8Ptr)
})

结果