如何声明自引用模板类型

Question

I've a situation that is like this contrived example:

template<class TFeature> struct Controller {};

template<class TController,typename T> struct Feature {
  typedef Feature<TController,T> FeatureType;
};

typedef Controller<Feature::FeatureType,int> DefaultController;

The Controller is templated to accept features and my problem is that some of the features need the type of the controller as a template parameter. This makes the typedef on the last line of the sample not compile.

Is this possible or do I need to rethink the design?

Answer 1

In order to accomplish this you should do some meta programming magic(and believe me it is not an easy task). But if you really nead it and using boost is an option for you take a look at boost::mpl and you can have something like this:

template< class ControlerT >
struct FeatureEx {
    typedef ControlerT controler_type;
};
template< class FeatureT >
struct ControlerEx {
    typedef ControlerEx<FeatureT> this_type;
    typedef typename boost::mpl::apply<
        FeatureT, boost::mpl::identity<this_type>
    >::type feature_type;

    feature_type const& get_feature() const {return f_;}

private:
    feature_type f_;
};

typedef ControlerEx<FeatureEx<boost::mpl::placeholders::_1> > DefaultControler;

Answer 2

You are passing to the Controller class two template parameters, but you have declared it to take only one. Do you need something like the following?

typedef Controller<Feature<Controller<int>,int>::FeatureType> DefaultController;

Answer 3

一种选择是使用虚拟子类而不是typedef：

struct DefaultController : public Controller<Feature<DefaultController,int>::FeatureType> {};

Answer 4

似乎你试图将2个参数传递给你的控制器模板，而它只能接受一个。