Making map double pair

Question

I have class:

template <typename _T, typename _E>
class CRoute
{ 
  public:
    CRoute& Add(const _T & u1 , const _T & u2 , const _E & e);
    ...
  private:
    map < _T, vector<pair<_T,_E>> > graf;
};

Add function have to assign elements to graf;

BUT! I can not use default constructor of _T and _E types. Because of this I can't do following:

template <typename _T, typename _E>
CRoute<_T,_E>& CRoute<_T,_E>::Add(const _T & u1 , const _T & u2 , const _E & e){      
     graf[u1].emplace_back( u2 , e );
     return *this;
}

I can use only copy constructor. How can I make it?

Your `graf` map's key-value-pair is `std::pair<_T, std::vector>`, you are trying to insert a `std::pair<_T, std::pair<_T, _E>>`. — user2296177, May 07 '16 at 17:19

score 0 · Answer 1 · answered May 07 '16 at 17:29

You could take inspiration from std::map::emplace_back and have your own Add function work the same way, taking arguments for constructing _T and _E objects, rather than already-constructed instances of those objects.

Otherwise your only option is to take rvalue references and hope your types are movable.

Making map double pair

1 Answers1