c++ - Mixin和接口(interface)实现

Question

根据 http://www.thinkbottomup.com.au/site/blog/C%20%20_Mixins_-_Reuse_through_inheritance_is_good

But hang on a minute, none of this helps us plug into our Task Manager framework as the classes do not implement the ITask interface. This is where one final Mixin helps - a Mixin which introduces the ITask interface into the inheritance hierarchy, acting as an adapter between some type T and the ITask interface:

template< class T >
class TaskAdapter : public ITask, public T
{
public:
    virtual void Execute()
    {
        T::Execute();
    }

    virtual std::string GetName()
    {
        return T::GetName();
    }
};

Using the TaskAdapter is simple - it's just another link in the chain of mixins.

// typedef for our final class, inlcuding the TaskAdapter<> mixin
typedef public TaskAdapter< 
                    LoggingTask< 
                        TimingTask< 
                            MyTask > > > task;

// instance of our task - note that we are not forced into any heap allocations!
task t;

// implicit conversion to ITask* thanks to the TaskAdapter<>
ITask* it = &t;
it->Execute();

当 ITask 由 MyTask 实现时，为什么需要 TaskAdapter？另外如果ITask不是抽象的，可能会导致菱形问题。

Answer 1

那是一篇非常很酷很有趣的文章。

在最后一个 Mixin 示例中，MyTask 类不是派生自 ITask。这意味着它不能转换为在最后完成的 ITask 指针。

在该示例中，我相信您可以从 ITask 派生 MyTask。但我认为作者想说明您甚至可以使用 TaskAdapter 解耦 MyTask 类。