c++ - how to emplace_back(pair) efficiently? -

i have

using namespace std;   // convenience in question vector<pair<array<int,3>, int>> foo; 

and want emplace_back element pair::first holding {i,j,k} , pair::second holding q. way compiling rather clumsy

foo.emplace_back(piecewise_construct,                  forward_as_tuple(i,j,k),                  forward_as_tuple(q)); 

is efficient (i.e. guaranteed tuples optimised away)? or there way guaranteed efficient?

(i tried

foo.emplace_back(std::initializer_list<int>{i,j,k}, q); 

but no avail gcc 4.8.1). know can avoid problem defining

struct element : std::pair<std::array<int,3>,int> {   element(int i, int j, int k, int q)   { first={i,j,k}; second=q; } };  vector<element> foo; foo.emplace_back(i,j,k,q); 

but i'd prefer without such code.

std::array<t, n> doesn't have constructor taking std::initializer_list<u> u, not u = t. don't mistake fact can initialised braced-init-list presence of such constructor.

instead, create array.

foo.emplace_back(std::array<int,3>{i,j,k}, q); 

there hardly guarantees efficiency, , not guaranteed more efficient tuple approach. in practice, shouldn't make of difference, expect implementations optimise both forms of emplace_back same machine code. if care, , doubt that, measure it.