OBJECTIVE-C Kit Kat Kinky Technology--ims

Artifice refers to a skill and a product that is too kit and useless.
IMS refers to Instance method swizzling, which is confused by instance methods.
The next section of code is an example of a instance method swizzling and a method swizzling:

// Man.m
-(void) run
{
     NSLog (@ "% s,% @", __func__, _name);
}
-(void) jump
{
     NSLog (@ "% s,% @", __func__, _name);
}
-(void) handsUp
{
     NSLog (@ "% s,% @", __func__, _name);
}
-(void) handsDown
{
     NSLog (@ "% s,% @", __func__, _name);
}

// ViewController.m
-(void) viewDidLoad {
     ...
     Man * a = [Man manWithName: @ "a"];
     Man * b = [Man manWithName: @ "b"];

     [self swizzleInstanceMethodWithInstance: a originalSel: @selector (run) replacementSel: @selector (jump)];
     [self swizzleInstanceMethodWithClass: [Man class] originalSel: @selector (handsUp) replacementSel: @selector (handsDown)];

     [a run];
     [b run];

     [a handsUp];
     [b handsUp];
}


// The output is
2015-03-14 23: 53: 39.832 testRuntime [2196: 629365]-[Man jump], a
2015-03-14 23: 53: 39.833 testRuntime [2196: 629365]-[Man run], b
2015-03-14 23: 53: 39.833 testRuntime [2196: 629365]-[Man handsDown], a
2015-03-14 23: 53: 39.833 testRuntime [2196: 629365]-[Man handsDown], b 

Why is the Run method only replaced with object A, and the Handsup method is all replaced?
Let's start by looking at how the common method swizzling is implemented.

-(void) swizzleInstanceMethodWithClass: (Class) clazz originalSel: (SEL) original replacementSel: (SEL) replacement
{
     Method a = class_getInstanceMethod (clazz, original);
     Method b = class_getInstanceMethod (clazz, replacement);
     // class_addMethod adds a new method to the class
     if (class_addMethod (clazz, original, method_getImplementation (b), method_getTypeEncoding (b)))
     {
         // Replace the implementation pointer of the class method
         class_replaceMethod (clazz, replacement, method_getImplementation (a), method_getTypeEncoding (a));
     }
     else
     {
         // exchange implementation pointers for 2 methods
         method_exchangeImplementations (a, b);
     }
} 

Instance method Swizzling is a method similar to KVO.
Dynamically add a class MySubClass inherit from the original class, then modify the Isa for object A to be the new class, and then replace the method of the new class.

 
- (void)swizzleInstanceMethodWithInstance:(id)object originalSel:(SEL)original replacementSel:(SEL)replacement
{
    Class newClass = objc_allocateClassPair([object class], "MySubclass", 0);
    objc_registerClassPair(newClass);

    Method a = class_getInstanceMethod(newClass, original);
    Method b = class_getInstanceMethod([object class], replacement);
    if (class_addMethod(newClass, original, method_getImplementation(b), method_getTypeEncoding(b))) {
        class_replaceMethod(newClass, replacement, method_getImplementation(a), method_getTypeEncoding(a));
    }
    else
    {
        method_exchangeImplementations(a, b);
    }

    object_setClass(object, newClass);
}

OBJECTIVE-C Kit Kat Kinky Technology--ims