How to get element from std::tuple by type

Question

I have a set of classes A, B, C and I want to have access instances of them from generic code by type, f.e

template
newObject()
{
    retur         


        

Answer 1

You can also compute the position of the type with a constexpr function if you don't like template.

  constexpr int count_first_falses() { return 0; }

  template 
  constexpr int count_first_falses(bool b1, B... b)
  {
    if (b1) return 0;
    else return 1 + count_first_falses(b...);
  }

  template 
  decltype(auto) tuple_get_by_type(const std::tuple& tuple)    
  {
    return std::get::value)...)>(tuple);
  }