objc访问类的私有API

CallPrivate *p = [[CallPrivate alloc]init];
    NSString *selStr = @"readMoney";
    SEL selector = NSSelectorFromString(selStr);
    Method methond = class_getInstanceMethod([p class], selector);
    IMP imp = method_getImplementation(methond);
    void(*perform)() = (void*)imp;
    perform();

 readMoney是CallPrivate的一个instance函数，这里面有一个限制，限制是readMoney函数中不能读写CallPrivate类的成员变量。