C++ Insights

Source:

#include <iostream>

using namespace std;

struct Nil {};

template <typename T1 = Nil, typename T2 = Nil>
struct Tuple1 : Tuple1<T2>
{
  T1 x;

using Base = Tuple1<T2>;

Base* base() { return static_cast<Base*>(this); }
  const Base* base() const { return static_cast<const Base*>(this); }

Tuple1(const T1& t1, const T2& t2)
    : Base{ t2 }, x{ t1 } {}
};

template <> struct Tuple1<> {};

template <typename T1>
struct Tuple1<T1> : Tuple1<>
{
  T1 x;

using Base = Tuple1<>;

Base* base() { return static_cast<Base*>(this); }
  const Base* base() const { return static_cast<const Base*>(this); }

Tuple1(const T1& t1)
    : Base{}, x{ t1 } {}
};

// ---------------------------------------------------------------------------

template <typename...> struct Tuple2;

template <> struct Tuple2<> {};

template <typename Head, typename... Tail>
struct Tuple2<Head, Tail...> : Tuple2<Tail...>
{
  Tuple2(const Head& head, const Tail&... tail)
    : Base{ tail... }, m_head{ head } {}

private:
  using Base = Tuple2<Tail...>;
  Head m_head;
};

int main()
{
  cout << "Tuple1 sizes:\n";
  cout << sizeof(Tuple1<>) << '\n';
  cout << sizeof(Tuple1<int*>) << '\n';
  cout << sizeof(Tuple1<int*, Nil>) << '\n';

cout << '\n';

cout << "Tuple2 sizes:\n";
  cout << sizeof(Tuple2<>) << '\n';
  cout << sizeof(Tuple2<int*>) << '\n';
  cout << sizeof(Tuple2<int*, Nil>) << '\n';

return 0;
}

Source:

Insight:

Console: