An assignment problem C ++ template class

For the following class template, if you want to achieve class assignment, use the assign () function. as follows

template<class T>
class MyClass{
private:
    T value;
public:
    void setValue(T& _value){
        value = _value;
    }
    void assign(const MyClass<T> &x){
        value = x.value;
    }
    T getValue(){
        return value;
    }
};
int main(void)
{
    MyClass<double> d;
    MyClass<double> dd;
    double temp=23.123;
    d.setValue(temp);
    dd.assign(d);
    cout << d.getValue() << endl << dd.getValue() << endl;
    return 0;
}

If two classes T is not the same, then use assign () method assignment

int main(void)
{
    MyClass<double> d;
    MyClass<int> i;
    double temp=23.123;
    d.setValue(temp);
    i.assign(d);
    cout << d.getValue() << endl << i.getValue() << endl;
    return 0;
}

Questions are as follows

You can see, assign () function is the desire to target a const MyClass <int> type as an argument, but got a MyClass <double> object. Meanwhile MyClass <double> can not be converted into const MyClass <int>, then the compiler will report an error.

 

We need to redefine what MyClass assign the function, so that the above assignment do the same.

    Template < class X-> // Add X-
     void ASSIGN ( const MyClass <X-> & x) {// the assignment x to be defined as another type of X- 
        value = x.getValue (); 
    }

Thus, the above assignment can work.

As long as from X to T assignment can be performed, then this assign function can be performed. In fact, this is to avoid having to assign a function to make parameter T must assign the object belongs to T  same.