How to write destructor for union-like class

Question

I\'m trying to use an union (C++) that has some non-primitive variables, but I\'m stuck trying to create the destructor for that class. As I have read, it is not possible to

Answer 1

If you want to use std::string in a union in C++11, you have to explicitly call its destructor, and placement new to construct it. Example from cppreference.com:

#include 
#include 
#include 
union S {
    std::string str;
    std::vector vec;
    ~S() {} // needs to know which member is active, only possible in union-like class 
}; // the whole union occupies max(sizeof(string), sizeof(vector))

int main()
{
    S s = {"Hello, world"};
    // at this point, reading from s.vec is UB
    std::cout << "s.str = " << s.str << '\n';
    s.str.~basic_string();
    new (&s.vec) std::vector;
    // now, s.vec is the active member of the union
    s.vec.push_back(10);
    std::cout << s.vec.size() << '\n';
    s.vec.~vector();
}