objective-c - ARC下，__weak 是否會改變物件的參考計數

Question

ARC環境下，事例代碼如下

    id __strong obj0 = [[NSObject alloc] init];
    id __weak obj = obj0;
    NSLog(@"obj0 :%p --- %ld", obj0, CFGetRetainCount((__bridge CFTypeRef) obj0));
    NSLog(@"obj  :%p --- %ld", obj, CFGetRetainCount((__bridge CFTypeRef) obj));

列印結果如下
2015-11-29 22:19:14.753 Test[15256:150713] obj0 :0x7f9f92d15d00 --- 1
2015-11-2912d15d00 --- 1

2015-11-29121515:505 7f9f92d15d00 -- - 3

這個3是怎麼來的呢？ 🎜