@interface Person : NSObject
-(void)test;
@end
@implementation Person
-(void)test{
    NSLog(@"test");
}
int main(int argc, const char * argv[]) {
    @autoreleasepool {
        Person *p = [Person new];
        //手动的把test包装成SEL类型
        SEL s1= @selector(test);
         [p performSelector:s1];
        //这两句相当于[p test];
    }
    return 0;
}

[p performSelector:s1]  等效于 [p performSelector:@selector(test)]