/** 
* Adds a new method to a class with a given name and implementation.
* 
* @param cls The class to which to add a method.
* @param name A selector that specifies the name of the method being added.
* @param imp A function which is the implementation of the new method. The function must take at least two arguments—self and _cmd.
* @param types An array of characters that describe the types of the arguments to the method. 
* 
* @return YES if the method was added successfully, otherwise NO 
* (for example, the class already contains a method implementation with that name).
*
* @note class_addMethod will add an override of a superclass's implementation, 
* but will not replace an existing implementation in this class. 
* To change an existing implementation, use method_setImplementation.
*/
OBJC_EXPORT BOOL class_addMethod(Class cls, SEL name, IMP imp, 
const char *types) 
__OSX_AVAILABLE_STARTING(__MAC_10_5, __IPHONE_2_0);

Class cls

SEL name

IMP imp

const char *types

#import "Car+myCar.h"
@implementation Car (myCar)
@end

+ (BOOL)resolveInstanceMethod:(SEL)sel
+ (BOOL)resolveClassMethod:(SEL)sel

#import "Car+myCar.h"
void startEngine(id self, SEL _cmd) {
NSLog(@"my car starts the engine");
}
@implementation Car (myCar)
@end

#import "Car+myCar.h"
void startEngine(id self, SEL _cmd, NSString *brand) {
NSLog(@"my %@ car starts the engine", brand);
}
@implementation Car (myCar)
@end

#import "Car+myCar.h"
#import <objc/runtime.h>
void startEngine(id self, SEL _cmd, NSString *brand) {
NSLog(@"my %@ car starts the engine", brand);
}
@implementation Car (myCar)
+ (BOOL)resolveInstanceMethod:(SEL)sel {
if (sel == @selector(drive)) {
class_addMethod([self class], sel, (IMP)startEngine, "v@:@");
return YES;
}
return [super resolveInstanceMethod:sel];
}
@end

@implementation Car (myCar)
+ (BOOL)resolveInstanceMethod:(SEL)sel {
if (sel == @selector(drive)) {
class_addMethod([self class], sel, class_getMethodImplementation(self, @selector(startEngine:)), "s@:@");
return YES;
}
return [super resolveInstanceMethod:sel];
}
- (void)startEngine:(NSString *)brand {
NSLog(@"my %@ car starts the engine", brand);
}
@end

#import "DynamicSelector.h"
#import "Car+myCar.h"
@implementation DynamicSelector
- (void)dynamicAddMethod {
Car *c = [[Car alloc] init];
[c performSelector:@selector(drive) withObject:@"bmw"];
}
@end

2016-08-26 10:50:17.207 objc-runtime[76618:3031897] my bmw car starts the engine
Program ended with exit code: 0