SFINAE and concept comparison

sfinae-concept.cpp

#include <concepts>
#include <iostream>
#include <type_traits>

struct BothAssignable {
  constexpr auto operator=(const BothAssignable&) noexcept -> BothAssignable& = default;
  constexpr auto operator=(BothAssignable&&) noexcept -> BothAssignable& = default;
};

struct CopyAssignable {
  constexpr auto operator=(const CopyAssignable&) noexcept -> CopyAssignable& = default;
  constexpr auto operator=(CopyAssignable&&) noexcept -> CopyAssignable& = delete;
};

struct MoveAssignable {
  constexpr auto operator=(const MoveAssignable&) noexcept -> MoveAssignable& = delete;
  constexpr auto operator=(MoveAssignable&&) noexcept -> MoveAssignable& = default;
};

template <typename T,
          typename std::enable_if_t<!std::is_move_assignable_v<T> &&
                                        std::is_copy_assignable_v<T>,
                                    bool> = true>
auto func_sfinae() -> void {
  std::cout << "is_copy_assignable\n";
}

template <typename T,
          typename std::enable_if_t<std::is_move_assignable_v<T>, bool> = false>
auto func_sfinae() -> void {
  std::cout << "is_move_assignable\n";
}

template <typename T>
  requires (!std::is_move_assignable_v<T> && std::is_copy_assignable_v<T>)
auto func_concept() -> void {
  std::cout << "is_copy_assignable\n";
}

template <typename T>
  requires std::is_move_assignable_v<T>
auto func_concept() -> void {
  std::cout << "is_move_assignable\n";
}

auto main() -> int {
  func_sfinae<BothAssignable>();  // is_move_assignable
  func_sfinae<CopyAssignable>();  // is_copy_assignable
  func_sfinae<MoveAssignable>();  // is_move_assignable
  func_concept<BothAssignable>(); // is_move_assignable
  func_concept<CopyAssignable>(); // is_copy_assignable
  func_concept<MoveAssignable>(); // is_move_assignable
}