Swift vs ObjC初始化过程？ [英] Swift vs ObjC initialisation process?

问题描述

在ObjectiveC中我们创建对象，如

In ObjectiveC we create objects like

 -(instancetype)init()
{
  return [super init]; // Here it returns initialised value
}  

Class *obj =   [[Class alloc]init] 

但swift初始化器不会返回任何值。

But swift initialiser wont return any value.

来自Swift文档

与Objective-C初始值设定项不同，Swift初始值设定项不返回值。它们的主要作用是确保在第一次使用之前正确初始化类型的新实例。

Unlike Objective-C initializers, Swift initializers do not return a value. Their primary role is to ensure that new instances of a type are correctly initialized before they are used for the first time.

init()
{
  super.init()
}  

let obj = Class()

现在swift初始化器如何将实例返回到变量 obj ？。

Now how swift initialiser returns the instance to variable obj?.

如何在swift中发生 分配和初始化 ？

How the allocation and initialisation occurs in swift?

推荐答案

这只是一个惯例。 Swift初始化器设置一个有效的实例，理论上无法返回任何其他有效实例，因此明确返回没有任何意义。

It's just a convention. Swift initialiser sets up a valid instance and could not theoretically return anything other that a valid instance, so there's no point in explicit return.

所以（从我的观点来看）分配&初始化序列如下所示：

So (from my point of view) allocation & initialisation sequence looks like this:

1. 运行时分配所请求类的实例


2. 使用<调用初始化程序code> self 设置为已分配的实例


3. 初始化程序执行设置


4. 运行时将初始化的实例返回给客户端代码

1. Runtime allocates instance of requested class
2. Initializer is called with self set to allocated instance
3. Initializer performs setup
4. Runtime returns initialised instance to client code

虽然这种做法打破了一些有用的Objective-C模式，比如初始化者返回 nil 错误，实例化总是成功的保证允许编译器执行一些优化。同样没有丢弃初始化者返回 nil ，实际上不可能从语言中删除 nil ，如果初始化者是返回期权。

Although this approach breaks some useful Objective-C patterns like initialisers returning nil on error, the guarantee that instantiation always succeeds allows compiler to perform some optimisations. Also without dropping initialisers returning nil it would be impossible to actually remove nil from language, it would seem weird if initialisers were returning optionals.

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