View source for Template:cpp/synopsis/expected

====Class template {{lc|std::expected}}====
{{source|1=
namespace std {
  template<class T, class E>
  class expected {
  public:
    using value_type = T;
    using error_type = E;
    using unexpected_type = unexpected<E>;

    template<class U>
    using rebind = expected<U, error_type>;

    // constructors
    constexpr expected();
    constexpr explicit(/* see description */) 
      expected(const expected&);
    constexpr explicit(/* see description */) 
      expected(expected&&) noexcept(/* see description */);
    template<class U, class G>
      constexpr explicit(/* see description */) expected(const expected<U, G>&);
    template<class U, class G>
      constexpr explicit(/* see description */) expected(expected<U, G>&&);

    template<class U = T>
      constexpr explicit(/* see description */) expected(U&& v);

    template<class G>
      constexpr expected(const unexpected<G>&);
    template<class G>
      constexpr expected(unexpected<G>&&);

    template<class... Args>
      constexpr explicit expected(in_place_t, Args&&...);
    template<class U, class... Args>
      constexpr explicit expected(in_place_t, initializer_list<U>, Args&&...);
    template<class... Args>
      constexpr explicit expected(unexpect_t, Args&&...);
    template<class U, class... Args>
      constexpr explicit expected(unexpect_t, initializer_list<U>, Args&&...);

    // destructor
    constexpr ~expected();

    // assignment
    constexpr expected& operator=(const expected&);
    constexpr expected& operator=(expected&&) noexcept(/* see description */);
    template<class U = T> constexpr expected& operator=(U&&);
    template<class G>
      constexpr expected& operator=(const unexpected<G>&);
    template<class G>
      constexpr expected& operator=(unexpected<G>&&);

    template<class... Args>
      constexpr T& emplace(Args&&...) noexcept;
    template<class U, class... Args>
      constexpr T& emplace(initializer_list<U>, Args&&...) noexcept;

    // swap
    constexpr void swap(expected&) noexcept(/* see description */);
    friend constexpr void swap(expected&, expected&) noexcept(/* see description */);

    // observers
    constexpr const T* operator->() const noexcept;
    constexpr T* operator->() noexcept;
    constexpr const T& operator*() const& noexcept;
    constexpr T& operator*() & noexcept;
    constexpr const T&& operator*() const&& noexcept;
    constexpr T&& operator*() && noexcept;
    constexpr explicit operator bool() const noexcept;
    constexpr bool has_value() const noexcept;
    constexpr const T& value() const&;
    constexpr T& value() &;
    constexpr const T&& value() const&&;
    constexpr T&& value() &&;
    constexpr const E& error() const&;
    constexpr E& error() &;
    constexpr const E&& error() const&&;
    constexpr E&& error() &&;
    template<class U> constexpr T value_or(U&&) const&;
    template<class U> constexpr T value_or(U&&) &&;
    template<class G = E> constexpr E error_or(G&&) const &;
    template<class G = E> constexpr E error_or(G&&) &&;

    // monadic operations
    template<class F> constexpr auto and_then(F&& f) &;
    template<class F> constexpr auto and_then(F&& f) &&;
    template<class F> constexpr auto and_then(F&& f) const &;
    template<class F> constexpr auto and_then(F&& f) const &&;
    template<class F> constexpr auto or_else(F&& f) &;
    template<class F> constexpr auto or_else(F&& f) &&;
    template<class F> constexpr auto or_else(F&& f) const &;
    template<class F> constexpr auto or_else(F&& f) const &&;
    template<class F> constexpr auto transform(F&& f) &;
    template<class F> constexpr auto transform(F&& f) &&;
    template<class F> constexpr auto transform(F&& f) const &;
    template<class F> constexpr auto transform(F&& f) const &&;
    template<class F> constexpr auto transform_error(F&& f) &;
    template<class F> constexpr auto transform_error(F&& f) &&;
    template<class F> constexpr auto transform_error(F&& f) const &;
    template<class F> constexpr auto transform_error(F&& f) const &&;

    // equality operators
    template<class T2, class E2> requires (!is_void_v<T2>)
      friend constexpr bool operator==(const expected& x, const expected<T2, E2>& y);
    template<class T2>
      friend constexpr bool operator==(const expected&, const T2&);
    template<class E2>
      friend constexpr bool operator==(const expected&, const unexpected<E2>&);

  private:
    bool has_val;       // exposition only
    union {
      T val;            // exposition only
      E unex;           // exposition only
    };
  };
}
}}