Autorelease 然后为 setter 保留 [英] Autorelease then retain for setters

问题描述

根据 Google Objective-C 样式指南，我们应该自动释放然后保留:

According to the Google Objective-C Style Guide, we should autorelease then retain as so:

- (void)setFoo:(GMFoo *)aFoo {
  [foo_ autorelease];  // Won't dealloc if |foo_| == |aFoo|
  foo_ = [aFoo retain];
}

在这种情况下，如果 foo_ 被设置为同一个实例，则不会被释放，从而形成一个更具防御性的 setter.

In this case, foo_ will not be deallocated if being set to the same instance, making for a more defensive setter.

我的问题是，这是@property &@synthesize 工作吗?

My question is, is this how @property & @synthesize work?

推荐答案

release 由于 autorelease 直到当前 runloop 结束才会被调用，所以 foo_ 不会解除分配，因为首先调用 retain ，然后在最后调用 release当前运行循环.但是，这不是@synthesize 中生成的代码的工作方式.它更像

release due to an autorelease isn't called until the end of the current runloop so foo_ wont dealloc because retain is called first followed by release at the end of the current runloop. However, this isn't how the code generated in @synthesize works. It works more like

- (void)setFoo:(GMFoo *)aFoo {
   if (aFoo != foo_) {
      [aFoo retain];
      [foo_ release];
      foo_ = aFoo;
   } 
}

此方法在不需要更改时节省了 cpu 周期，并消除了使用自动释放池的小开销.

This method saves cpu cycles when no change is necessary and takes out the small overhead of using the autorelease pool.

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