具有特定模板化类的模板专业化

Question

Given the following simple C++ class:

using namespace std;

template<class T1>
class ValueWrapper {
private:
    T1 value_;

public:
    ValueWrapper() {} 
    ValueWrapper(const T1& value) {
        value_ = value;     
    }

    ValueWrapper(const ValueWrapper<T1> &wrapper) {
        value_ = wrapper.value_;
    }

    ValueWrapper& Set(const T1& value) {
        value_ = value;
        return *this;
    }

    T1 Get() const {
        return value_;
    }
};

I was trying to create a simple shared_ptr wrapper for that class (ultimately allowing the developer to use the class without the dereferencing operator if desired). While I've seen a few examples of wrapping a shared_ptr , I couldn't find any that also used a specialization for a templated class.

Using the class above, I created a ValueShared class which derives from shared_ptr :

template<class T1>
class ValueShared : public shared_ptr<T1> {
public:
    ValueShared& operator =(const T1& rhs) {
        // nothing to do in base
    return *this;
    }
};

Then, I created a custom make_shared_value function:

//
// TEMPLATE FUNCTION make_shared
template<class T1, class... Types> inline
ValueShared<T1> make_shared_value(Types&&... Arguments)
{   // make a shared_ptr
    _Ref_count_obj<T1> *_Rx = new _Ref_count_obj<T1>(_STD forward<Types>(Arguments)...);

    ValueShared<T1> _Ret;
    _Ret._Resetp0(_Rx->_Getptr(), _Rx);
    return (_Ret);
}

But, here's the problem code:

template<class T1, class ValueWrapper<T1>> 
class ValueShared<ValueWrapper<T1>> : public shared_ptr<ValueWrapper<T1>>{
    public:
        ValueShared& operator =(const ValueWrapper<T1>& rhs) {              
            auto self = this->get();
            self.Set(rhs->Get());
            return *this;
        }
};

I wanted to provide a specialization of the equals operator here that was specialized to the ValueWrapper class (so that it would Get/Set the value from the right hand side value).

I've tried a few things, but the current error is:

error C2943: 'ValueWrapper<T1>' : template-class-id redefined
as a type argument of a template

Maybe this isn't the proper approach, or maybe it's not possible?

Answer 1

Following should remove your error:

template<class T1>
class ValueShared<ValueWrapper<T1>> : public shared_ptr<ValueWrapper<T1>> {
    public:
        ValueShared& operator =(const ValueWrapper<T1>& rhs)
        {
            auto self = this->get();
            self->Set(rhs.Get());
            return *this;
        }
};