专门用于联合类型的C ++模板方法

Question

Suppose I have a union:

union U{
    int i;
    float f;
};

I want to write a generic method that uses it as a float or int. Something like this:

template <typename T>
T sum(std::vector<U> vec){
    T res(0);
    for (U &v: vec){
        res += ... // use v.i or v.f depending on what T is
    }
    return res;
}

Is there a way to do this? This was just an example method. I have a much longer, complicated method, and I don't want to duplicate it just to switch which union type it is using.

Answer 1

Specialization would work:

template <typename T> T const & get(U const &);

template <> int const & get<int>(U const & u) { return u.i; }
template <> float const & get<float>(U const & u) { return u.f; }

Usage:

for (U & v : vec) { res += get<T>(v); }