Objective-C: Empty segment Selector

Objective-C: Empty segment Selector

Prelude

Objective-C has a personality. A distinctive feature is that method functions are segmented, that is, function names are not written together, but are split into N segments, which correspond to N parameters respectively, this greatly increases the readability of the Code.

#define WQ_FUNC_LOG NSLog(@"%s",__FUNCTION__)- (void)firstSegment:(id)firstObj secSegment:(id)secObj thirdSegment:(id)thirdObj{    WQ_FUNC_LOG;}

For convenience, I printed my method name in this method. After this signal is sent (generally this method is called)

 - (void)viewDidLoad{    [super viewDidLoad];              [self firstSegment:@"1" secSegment:@"2" thirdSegment:@"3"];}

We will get the following log output. We can clearly see that the selector name is firstsegment: secsegment: thirdsegment:

2013-07-05 16:34:13.977 Test[1828:c07] -[WQTestViewController firstSegment:secSegment:thirdSegment:]

Topic

OK. The prelude is complete. Enter the topic. If I delete the second parameter secobj in the function prototype, what will happen?

- (void)firstSegment:(id)firstObj secSegment:(id) thirdSegment:(id)thirdObj{    WQ_FUNC_LOG;}

If you use the xcode auto-completion method, you will find that

 - (void)viewDidLoad{    [super viewDidLoad];              [self firstSegment:@"1" secSegment:@"2" :@"3"];}

Run the following log:

2013-07-05 17:26:10.725 Test[1976:c07] -[WQTestViewController firstSegment:secSegment::]

The conclusion is that the method is declared as firstsegment: secsegment:. What about the parameter? Of course, it is not difficult to guess and verify.

- (void)firstSegment:(id)firstObj secSegment:(id) thirdSegment:(id)thirdObj{    WQ_FUNC_LOG;    NSLog(@"args[] = {%@ ,%@, %@};",firstObj,thirdSegment,thirdObj);}

When thirdsegment and thirdobj are both considered as parameters, we have to have such a bold conjecture: Can selector support empty segments? Does selector have no name?
Try to create a method without a name. The correct statement is that an empty Selector

- (void) :(id)obj{}- (void)viewDidLoad{    [super viewDidLoad];        SEL sel = @selector(:);    if ([self respondsToSelector:sel]) {        NSLog(@"ur right");    }}

Compile and run the program. The log output tells us that our conjecture is correct. Objective-C supports the null selector.

Conclusion

Objective-C supports empty segments selector, which obviously does not have good code readability. We usually do not use it like this. Why do we need to mention this? I just want to remind you that sometimes we may encounter a low-level bug that requires debugging for a long time due to carelessness or carelessness. In particular, the delegate method is named smelly and long ......