Question

I enabled zombies with my Xcode to find if my process crashes to a memory leak. Here is a code snippet:

- (NSString *)facVersion
{
    return facVersion;
}


- (void) setFacVersion:(NSString*)_facVersion
{
    if(facVersion != nil) [facVersion release];
    facVersion = [_facVersion retain];
}

Now when I call

NSLog(@"%@", facVersion);
[self setFacVersion:facVersion];

the code crashes with the message

[CFString retain]: message sent to deallocated

Do you know what the problem is?

Answer 1

This is a typical problem with badly written setters. When the object itself is the last owner of the backing ivar of the property, assigning the property to itself causes a release effectively deallocating the object, then a retain on the same deallocated object. You can fix this in two ways. Either check for the to-be-assigned object not being the same as the current value of the property, or retain first and release only after. All in all, solution one:

- (void) setFacVersion:(NSString*)_facVersion
{
    if (facVersion == _facVersion) return;
    [facVersion release];
    facVersion = [_facVersion retain];
}

Soltion two:

- (void) setFacVersion:(NSString*)_facVersion
{
    [_facVersion retain];
    [facVersion release];
    facVersion = _facVersion;
}

By the way, checking for an object not being nil before releasing it is superfluous. Objective-C is not Java.