Why isn’t my weak reference cleared right after the strong ones are gone?

Question

I am a little bit stubborn, but I want to understand weak and strong references well, so that's why I'm asking you once again. Consider this: ``` __weak NSString* mySecondPointer = myText; NSLog(@"myText: %@", myText); ``` The result is `myText: (null)` and it is pretty obvious - weak reference is set to null just after assignment, cause there is no strong reference to the pointed object. But in this case: ``` __strong NSString* strongPtr = [[NSString alloc] initWithFormat:@"mYTeSTteXt %d"]; // weak pointer points to the same object as strongPtr __weak NSString* weakPtr = strongPtr; if(strongPtr == weakPtr) NSLog(@"They are pointing to the same obj"); NSLog(@"StrongPtr: %@", strongPtr); NSLog(@"weakPtr: %@", weakPtr); NSLog(@"Setting myText to different obj or nil"); // after line below, there is no strong referecene to the created object: strongPtr = [[NSString alloc] initWithString:@"abc"]; // or myText=nil; if(strongPtr == weakPtr) NSLog(@"Are the same"); else NSLog(@"Are NOT the s…

Accepted Answer

From the assembly code it can be seen that accessing `weakPtr` generates a `objc_loadWeak` call.

According to the Clang documentation, `objc_loadWeak` retains and autoreleases the object and is equivalent to

```
id objc_loadWeak(id *object) {
  return objc_autorelease(objc_loadWeakRetained(object));
}
```

This (hopefully) explains why both

```
if(strongPtr == weakPtr) ...
```

and

```
NSLog(@"weakPtr: %@", weakPtr);
```

create additional autoreleased references.

This is not a special `NSString` problem, I could reproduce the same behaviour with a custom (plain) class.

Why isn’t my weak reference cleared right after the strong ones are gone?

Solution

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