Question

I am trying to achieve a very simple thing using C++ templates. I would like to build a generic sign function that could handle the case sgn(x)where x could be either doubleor std::vector<double> (that is returning a std::vector<double> containing the results). In order to achieve that I am using templates

double f(double x) {
    return (x>=0)?1.0:-1.0;
};

template<typename T>
T F(T x) {
   // ?
};

I would like to cast the template and either use f if double or a for loop if std::vector<double>. Unfortunately my function does not use any arithmetic operator and the conditional operator cannot be overloaded. How should I proceed ?

Answer 1

While overloading is the best way to achieve what you want, it is not
really the way to work with the C++ standard library.

If you want to apply a function to all elements of a container (either
mutating them or creating new results), use std::transform or
std::for_each with the function you want to use.

std::vector<double> doubles, results;
std::transform(begin(doubles), end(doubles), std::back_inserter(results), sgn);

That separates concern far better than your current approach. Only
operate on whole containers if it is really required, in all other
cases use iterators and higher-order functions.