消息分派器

Objective-C运行时的核心就在于消息分派器objc_msgSend

实现简单的消息分派器。以下代码用C编写，为了证明Objective-C运行时真的只是C。

static const void *myMsgSend(id receiver, const char *name) {
    SEL selector = sel_registerName(name);
    IMP methodIMP = class_getMethodImplementation(object_getClass(receiver), selector);
    return methodIMP(receiver, selector);
}

void RunMyMsgSend() {
    // NSObject *object = [[NSObject alloc] init];
    Class class = (Class)objc_getClass("NSObject");
    id object = class_createInstance(class, 0);
    myMsgSend(object, "init");
    
    // id description = [object description];
    id description = (id)myMsgSend(object, "description");
    
    // const char * cstr = [description UTF8String];
    const char *cstr = myMsgSend(description, "UTF8String");
    
    printf("%s\n",cstr);
}