objc_runtime/exchange_method, OC運行時交換方法

void OBJC_ExchangeMethod(Class c, SEL orig, SEL new) {
	Method origMethod = class_getInstanceMethod(c, orig);
	Method newMethod = class_getInstanceMethod(c, new);
	if (class_addMethod(c, orig, method_getImplementation(newMethod), method_getTypeEncoding(newMethod))) {
		class_replaceMethod(c, new, method_getImplementation(origMethod), method_getTypeEncoding(origMethod));
	} else {
		method_exchangeImplementations(origMethod, newMethod);
	}
}