c++ - How can I use a vector wrapper class when enclosed in another vector? -

consider free function third part library expects std::vector argument: void foo( std::vector<sometype>& );

now, write wrapper around type can add member functions. able use foo() type, add access function.

class wrapper {    private:       std::vector<sometype> _data;    public:        std::vector<sometype>& data() { return _data; }        const std::vector<sometype>& data() const { return _data; }        //... other stuff }; 

this way, can still use foo():

wrapper a; foo( a.data() ); 

but consider function, expects vector of vectors of sometype (edit: , adds elements vector) :

void bar( std::vector<std::vector<sometype>>& ); 

but datatype have std::vector<wrapper> vec;

is there way use wrapper type call bar() ? want this:

 std::vector<wrapper> vec;  bar( ??? ); 

the point want avoid first call bar() required type, , having copy 1 one elements vector<wrapper>.

at first, i'd "no", maybe there smart solution ?

edit2: give example, consider following toy implementation bar() int root datatype:

void bar( std::vector<std::vector<int>>& vv ) {    std::vector<int> v1 = { 1,2,3 };    std::vector<int> v2 = { 4,5,6 };    vv.push_back(v1);    vv.push_back(v2); } 

[edited after new comments requiring elements added in bar function] possible solution keep std::vector<std::vector<sometype>> function use , operate on vectoraccessor object referring real vectors

#include <iostream> #include <vector>  struct sometype {     int value;     sometype(int v) : value(v) {} };  void bar(std::vector<std::vector<sometype>>& par) {      std::cout << "bar() - before adding new elements:" << std::endl;     (auto& subvec : par) {         std::cout << "subvector: {";         (auto& sometypeitem : subvec) {             std::cout << sometypeitem.value << " ";         }         std::cout << "};" << std::endl;     }      std::vector<sometype> newitem = {32, 33};     par.emplace_back(newitem);  }  class vectoraccessor {     std::vector<std::vector<sometype>>& m_vec; public:     vectoraccessor(std::vector<std::vector<sometype>>& v) : m_vec(v) {}      template<typename v>     void addvector(v&& vec) {         static_assert(std::is_same<typename std::remove_reference<v>::type,              std::vector<sometype>>::value, "not right type");         m_vec.emplace_back(std::forward<v>(vec));     }      std::vector<sometype> accessvector(size_t index) {         return m_vec[index];     } };  int main(int argc, char ** argv) {      std::vector<std::vector<sometype>> vec;     vectoraccessor vacc(vec);       // add element through vector accessor     std::vector<sometype> firstvector = {42};     firstvector.emplace_back(52);     vacc.addvector(firstvector);      // call bar , add few elements     bar(vec);      // access stuff usual wrapper     std::cout << "elements added bar:" << std::endl;     std::cout << "subvector: {";     (auto& sometypeitem : vacc.accessvector(1)) {         std::cout << sometypeitem.value << " ";     }     std::cout << "};" << std::endl;      return 0; } 

example