Method tuple

extern/boost/boost/tuple/detail/tuple_basic.hpp:490–490

access_traits ::parameter_type takes non-reference types as const T&

// access_traits<T>::parameter_type takes non-reference types as const T&
  tuple() {}

  explicit tuple(typename access_traits<T0>::parameter_type t0)
    : inherited(t0, detail::cnull(), detail::cnull(), detail::cnull(),