Question

I would like to write an abstract base class

class func_double_double_t : public unary_function<double, double>
{
    virtual double operator()(double x) = 0;
};

and specialize it for several different types

class func_pow_t : public func_double_double_t
{
 public:
    func_pow_t(double exponent) : exponent_(exponent) {};
    virtual double operator()(double x) { return pow(x, exponent_); };
}

class func_exp_t : public func_double_double_t
...

and pass these to a function when necessary:

double make_some_calculation(double num, func_double_double_t f)
{
     return f(x);
}

But I can’t define an object of type func_double_double_t because it’s abstract. I can pass a pointer to the function, but using f like f->operator()(num) seems against the spirit of operator overloading in the first place. ((*f)(num) is better, but still.)

Is there way to make operator overloading and such abstraction play nicely together?

Answer 1

You can simply pass a reference into your function:

double make_some_calculation(double num, func_double_double_t& f)
{
    return f(x);
}