c++boostvectorboost-any

C++: How to create a vector storing vectors of any type?


I'd like to store vectors of any type in another vector. So, for example I have two vector instances, "std::vector v1" and "std::vector v2". And I would like to put them into a vector. I already tried like this:

std::vector<int> v1;
std::vector<std::string> v2;
std::vector< std::vector<boost::any> > vc;
vc.push_back(v1);

And several other ways, but nothing works. Do you know a possible solution?

Thanks!


Solution

  • Disclaimer: I don't recommend this.

    But if you insist, here is the beginnings of such an abomination:

    #include <vector>
    #include <memory>
    #include <functional>
    #include <boost/any.hpp>
    
    
    class any_vector
    {
      using any = boost::any;
      struct concept
      {
        virtual any at(std::size_t) = 0;
        virtual any at(std::size_t) const = 0;
        virtual ~concept() = default; 
      };
    
      template<class T>
        struct model : concept
        {
          model(std::vector<T> v) : _data(std::move(v)) {}
          virtual any at(std::size_t i) override { return boost::any(std::ref(_data.at(i))); }
          virtual any at(std::size_t i) const override { return boost::any(std::cref(_data.at(i))); }
          std::vector<T> _data;
        };
    
      concept& deref() { return *vec_; }
      concept const& deref() const { return *vec_; }
    
      std::unique_ptr<concept> vec_;
    
      public:
    
      boost::any at(std::size_t i) const { return deref().at(i); }
      boost::any at(std::size_t i) { return deref().at(i); }
    
      template<class T>
      any_vector(std::vector<T> v)
      : vec_(std::make_unique<model<T>>(std::move(v)))
      {}
    };
    
    int main()
    {
      any_vector a(std::vector<int> { 1, 2, 3 });
      any_vector b(std::vector<double> { 1.1, 2.2, 3.3 });
    
      std::vector<any_vector> va;
      va.push_back(std::move(a));
      va.push_back(std::move(b));
    
    
      auto anything = va.at(0).at(1);
      // how you deal with the resulting `any` is up to you!
    }
    

    Note that any_vector::at(x) will return a boost::any which will either contain a const-ref or a ref to some object.

    Writing useful code that deduces what the thing is and uses it is going to be a challenge...