constexpr auto | operator() (Fun &&fun, Tup &&tup) const noexcept(noexcept(tuple_apply_fn::impl(static_cast< Fun && >(fun), static_cast< Tup && >(tup), tuple_indices_t< Tup >{}))) -> decltype(tuple_apply_fn::impl(static_cast< Fun && >(fun), static_cast< Tup && >(tup), tuple_indices_t< Tup > |