std::make_tuple doesn't make references

Question

I\'ve been experimenting with std::tuple in combination with references:

#include 
#include 

int main() {
  int a,         


        

Answer 1

std::tie makes non-const references.

auto ref_tuple = std::tie(a,b); // decltype(ref_tuple) == std::tuple

For const references, you'll either want the std::cref wrapper function:

auto cref_tuple = std::make_tuple(std::cref(a), std::cref(b));

Or use a simply as_const helper to qualify the variables before passing them off to std::tie:

template
T const& as_const(T& v){ return v; }

auto cref_tuple = std::tie(as_const(a), as_const(b));

Or, if you want to get fancy, write your own ctie (reusing std::tie and as_const):

template
std::tuple ctie(Ts&... vs){
  return std::tie(as_const(vs)...);
}

auto cref_tuple = ctie(a, b);