How does IMP work in iOS - objective-c

Question

In order to understand IMP, I wrote some test codes and found a problem in the process of testing.
I got a surprise 😂
Here is the code.
#interface Test : NSObject
#property (nonatomic, copy) NSString *name;
#end
#implementation Test
- (NSString *)description{
return [[super description] stringByAppendingString:self.name];
}
- (void)dealloc{
NSLog(#"Test dealloc %#",self);
}
- (void)test:(NSString *)str{
NSLog(#"- (void)test %#",str);
}
+ (void)test:(NSString *)str{
NSLog(#"+ (void)test %#",str);
}
- (void)test{
NSLog(#"- (void)test");
}
+ (void)test{
NSLog(#"+ (void)test");
}
#end
#interface ViewController ()
#end
#implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
// IMP imp = [[Test new] methodForSelector:#selector(test:)];
// NSLog(#"%p",imp);
// IMP imp1 = [Test instanceMethodForSelector:#selector(test)];
IMP imp2 = [Test methodForSelector:#selector(test:)];
// NSLog(#"%p",imp2);
imp2();
NSLog(#"%p",imp2);
// imp2 = [Test methodForSelector:#selector(test)];
// imp2();
// imp();
// imp = [[Test new] methodForSelector:#selector(test:)];
// NSLog(#"%p",imp);
// imp();
// imp1();
// imp1();
// imp2();
// imp2();
// void (*func)(id,SEL,NSString *) = (void *)imp;
// func([Test class],#selector(test:),#"");
// void (*func1)(id,SEL,NSString *) = (void *)imp1;
// func1([Test class],#selector(test:),#"ha");
// void (*func2)(id,SEL,NSString *) = (void *)imp2;
// func2([Test class],#selector(test:),#"haha");
// Do any additional setup after loading the view, typically from a nib.
}
- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
There's no problem when I run a single IMP.But when I run more than one IMP will crash for BAC_ACCESS and it only happens with the function which has arguments.So，why it can work with one and crash with two.

Answer 1

Of course you have a crash, because you need path id, SEL and also NSString * where needed.
Better cast to actual function prototype to have compiler errors when you call it wrong, instead of using direct IMP variables.
Apple should forbid () operator for IMPs and declare is as void * instead.
But people rarely use IMP for direct method calls, so there is no complains.