Vittorio's overload_set

overload.h

#pragma once

#include <type_traits>
#include <utility>

#if __cplusplus >= 201703L

// C++17 has variadic using

template <typename... Fs>
struct overload_set : Fs...
{
  using Fs::operator()...;
};

#else

// C++14 has to do template recursion

template <typename... Fs> struct overload_set;

// Base case
template <typename F>
struct overload_set<F> : F
{
  using F::operator();

  template <typename FF>
  overload_set(FF&& f)
    : F{std::forward<FF>(f)}
  {}
};

// Recursive case
template <typename F, typename... Fs>
struct overload_set<F, Fs...> : F, overload_set<Fs...>
{
  using F::operator();
  using overload_set<Fs...>::operator();

  template <typename FF, typename... FFs>
  overload_set(FF&& f, FFs&&... rest)
    : F{std::forward<FF>(f)}
    , overload_set<Fs...>{std::forward<FFs>(rest)...}
  {}
};

#endif

template <typename... Fs>
inline auto overload(Fs&&... fs)
{
  return overload_set<std::remove_reference_t<Fs>...>(
      std::forward<Fs>(fs)...);
}