Im afraid, I cant write farsi at present because of lack of farsi font in the computer Im working with,
But, ..
Mhaji! Im realy wondered if you have another solution for mentioned question, and intrested in finding out the answer of the question and that would be kind if you give some help regard this problem.
I think this will be a k ind of trick! in your answer!

.... .. ....
maybe you dont mean a technical trick. maybe it is about a program t use this statement wisely!.
Im thinking generic but nothing appears !
I no longer can think so missed up.
But if I had more time I would solve it.

+ like any other operators or functions can do any thing you want, with its operands as arguments. I think x is the unknown part of the expression not +

template <class T>
class LabelNumerical : public ...
{
private:

T val;

public:

...

virtual const char* toString() const
{
std::ostringstream ss;
ss<< ( val + 0 );

static string s;
s.clear();
s.append(ss.str());

return s.c_str();
}

}; // end of class

// Ok, val will be treated as an integer and so toString has the desired effect here:
typedef LabelNumerical<unsigned char> LabelUChar;

typedef LabelNumerical<int> LabelInt; // Ok, + 0 has no effect

// BUT NOT: typedef LabelNumerical<string> LabelString; ! Compile time error !

(int) x

(double) x