parent_method.m

#import <Foundation/Foundation.h>
#import <objc/runtime.h>
#import <objc/message.h>

@interface MyParent : NSObject
- (NSInteger)fetchNumber;
@end

@implementation MyParent 
- (NSInteger)fetchNumber 
{
    return 1;
}
@end

@interface MyChild : MyParent
@end

@implementation MyChild
- (NSInteger)fetchNumber 
{
    return 2;
}
@end

int main(int argc, char *argv[]) 
{
    @autoreleasepool {
        id parent = [[MyParent alloc] init];
        NSLog(@"Parent: %ld", [parent fetchNumber]);
        
        id child = [[MyChild alloc] init];
        NSLog(@"Child: %ld", [child fetchNumber]);
        
        IMP childMethod = [child methodForSelector:@selector(fetchNumber)];
        IMP parentMethod = 
            class_getMethodImplementation([child superclass], @selector(fetchNumber));
        
        NSLog(@"Child method: %p", childMethod);
        NSLog(@"Parent method: %p", parentMethod);
        
        NSInteger (*func)(id, SEL) = (void *)parentMethod;
        NSInteger value = func(child, @selector(fetchNumber));
        
        NSLog(@"This should be equal to the parent's value: %ld", value);
    }
}