为什么在Objective-C中alloc和init被单独调用？ [英] Why are alloc and init called separately in Objective-C?

问题描述

注意：我对Objective-C比较陌生，并且来自Java和PHP。

Note: I'm relatively new to Objective-C and am coming from Java and PHP.

有人可以向我解释为什么我总是先分配和然后初始化一个实例？

Could someone explain to me why I always have to first allocate and then initialize an instance?

无法在init方法中这样做：

Couldn't this be done in the init methods like this:

+ (MyClass*)init {
    MyClass *instance = [MyClass alloc];
    [instance setFoo:@"bla"];

    return instance;
}

+ (MyClass*)initWithString:(NSString*)text {
    MyClass *instance = [MyClass init];
    [instance setFoo:text];

    return instance;
}
...

这只是一个从旧的C天或者有没有我看不到的东西？

Is this just a relict from the old C days or is there something that I'm not seeing?

我知道这不是一个问题，因为我可以总是调用alloc和init，但因为它是一个有点乏味我想至少知道为什么我这样做。

I know this isn't a problem as I could as well always call alloc and init, but since it's a bit tedious I'd like to at least know why I'm doing it.

我喜欢语言的表达性，但这是我的想要完全理解为了思考Objective-C的方式。

I'm liking the expressiveness of the language so far, but this is something that I want to fully understand in order to think the Objective-C way.

谢谢！

推荐答案

+ new结束向类发送一个+ alloc消息，并向-init消息发送从+ alloc返回的任何内容。

+new ends up sending an +alloc message to the class and an -init message to whatever comes back from +alloc.

NeXT离开Stepstone使用+新消息（这是一个Smalltalk想法）的惯例是，早期，他们遇到了他们想要能够多次初始化同一个对象的情况。

The reason that NeXT departed from Stepstone's convention of using the +new message (which was a Smalltalk idea) is that early on, they encountered situations where they wanted to be able to initialize the same object more than once.

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