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Standard library header <expected> (C++23)

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C++
Standard library headers

Dieser Header ist Teil der allgemeinen Utility-Bibliothek .

Inhaltsverzeichnis

Klassen

(C++23)
Ein Wrapper, der entweder einen erwarteten oder einen Fehlerwert enthält
(Klassentemplate)
(C++23)
dargestellt als unerwarteter Wert
(Klassentemplate)
(C++23)
Exception, die einen geprüften Zugriff auf einen expected anzeigt, der einen unerwarteten Wert enthält
(Klassentemplate)
(C++23)
In-place-Konstruktions-Tag für unerwartete Werte in expected
(Tag)

Übersicht 

// meistens freestanding
namespace std {
  // Klassen-Template unexpected
  template<class E>
  class unexpected;
  // Klassen-Template bad_expected_access
  template<class E>
  class bad_expected_access;
  // Spezialisierung für void
  template<>
  class bad_expected_access<void>;
  // In-place-Konstruktion von unexpected-Werten
  struct unexpect_t
  {
    explicit unexpect_t() = default;
  };
  inline constexpr unexpect_t unexpect{};
  // Klassen-Template expected
  template<class T, class E>
  class expected; // teilweise freestanding
  // Partielle Spezialisierung von expected für void-Typen
  template<class T, class E>
    requires is_void_v<T>
  class expected<T, E>; // teilweise freestanding
}

Klassentemplate std::unexpected 

namespace std {
  template<class E>
  class unexpected
  {
  public:
    // Konstruktoren
    constexpr unexpected(const unexpected&) = default;
    constexpr unexpected(unexpected&&)      = default;
    template<class Err = E>
    constexpr explicit unexpected(Err&&);
    template<class... Args>
    constexpr explicit unexpected(in_place_t, Args&&...);
    template<class U, class... Args>
    constexpr explicit unexpected(in_place_t, initializer_list<U>, Args&&...);
    constexpr unexpected& operator=(const unexpected&) = default;
    constexpr unexpected& operator=(unexpected&&)      = default;
    constexpr const E& error() const& noexcept;
    constexpr E& error() & noexcept;
    constexpr const E&& error() const&& noexcept;
    constexpr E&& error() && noexcept;
    constexpr void swap(unexpected& other) noexcept(/* siehe Beschreibung */);
    template<class E2>
    friend constexpr bool operator==(const unexpected&, const unexpected<E2>&);
    friend constexpr void swap(unexpected& x,
                               unexpected& y) noexcept(noexcept(x.swap(y)));
  private:
    E /*unex*/; // nur zur Darstellung
  };
  template<class E>
  unexpected(E) -> unexpected<E>;
}

Klassentemplate std::bad_expected_access 

namespace std {
  template<class E>
  class bad_expected_access : public bad_expected_access<void>
  {
  public:
    constexpr explicit bad_expected_access(E);
    constexpr const char* what() const noexcept override;
    constexpr E& error() & noexcept;
    constexpr const E& error() const& noexcept;
    constexpr E&& error() && noexcept;
    constexpr const E&& error() const&& noexcept;
  private:
    E /*unex*/; // nur zur Darstellung
  };
}

Klassentemplatespezialisierung std::bad_expected_access<void> 

namespace std {
  template<>
  class bad_expected_access<void> : public exception
  {
  protected:
    constexpr bad_expected_access() noexcept;
    constexpr bad_expected_access(const bad_expected_access&) noexcept;
    constexpr bad_expected_access(bad_expected_access&&) noexcept;
    constexpr bad_expected_access& operator=(const bad_expected_access&) noexcept;
    constexpr bad_expected_access& operator=(bad_expected_access&&) noexcept;
    constexpr ~bad_expected_access();
  public:
    constexpr const char* what() const noexcept override;
  };
}

Klassentemplate std::expected 

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>;
    // Konstruktoren
    constexpr expected();
    constexpr expected(const expected&);
    constexpr expected(expected&&) noexcept(/* siehe Beschreibung */);
    template<class U, class G>
    constexpr explicit(/* siehe Beschreibung */) expected(const expected<U, G>&);
    template<class U, class G>
    constexpr explicit(/* siehe Beschreibung */) expected(expected<U, G>&&);
    template<class U = remove_cv_t<T>>
    constexpr explicit(/* siehe Beschreibung */) expected(U&& v);
    template<class G>
    constexpr explicit(/* siehe Beschreibung */) expected(const unexpected<G>&);
    template<class G>
    constexpr explicit(/* siehe Beschreibung */) 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&&...);
    // Destruktor
    constexpr ~expected();
    // Zuweisung
    constexpr expected& operator=(const expected&);
    constexpr expected& operator=(expected&&) noexcept(/* siehe Beschreibung */);
    template<class U = remove_cv_t<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(/* siehe Beschreibung */);
    friend constexpr void swap(expected& x, expected& y) noexcept(noexcept(x.swap(y)));
    // Beobachter
    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&;   // freestanding-deleted
    constexpr T& value() &;              // freestanding-deleted
    constexpr const T&& value() const&&; // freestanding-deleted
    constexpr T&& value() &&;            // freestanding-deleted
    constexpr const E& error() const& noexcept;
    constexpr E& error() & noexcept;
    constexpr const E&& error() const&& noexcept;
    constexpr E&& error() && noexcept;
    template<class U = remove_cv_t<T>>
    constexpr T value_or(U&&) const&;
    template<class U = remove_cv_t<T>>
    constexpr T value_or(U&&) &&;
    template<class G = E>
    constexpr E error_or(G&&) const&;
    template<class G = E>
    constexpr E error_or(G&&) &&;
    // monadische Operationen
    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&&;
    // Gleichheitsoperatoren
    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 /*Wert*/;  // exposition-only
      E /*unex*/; // exposition-only
    };
  };
}

Partielle Spezialisierung von std::expected für void -Typen 

template<class T, class E>
  requires is_void_v<T>
class expected<T, E>
{
public:
  using value_type      = T;
  using error_type      = E;
  using unexpected_type = unexpected<E>;
  template<class U>
  using rebind = expected<U, error_type>;
  // Konstruktoren
  constexpr expected() noexcept;
  constexpr expected(const expected&);
  constexpr expected(expected&&) noexcept(/* siehe Beschreibung */);
  template<class U, class G>
  constexpr explicit(/* siehe Beschreibung */) expected(const expected<U, G>&);
  template<class U, class G>
  constexpr explicit(/* siehe Beschreibung */) expected(expected<U, G>&&);
  template<class G>
  constexpr explicit(/* siehe Beschreibung */) expected(const unexpected<G>&);
  template<class G>
  constexpr explicit(/* siehe Beschreibung */) expected(unexpected<G>&&);
  constexpr explicit expected(in_place_t) noexcept;
  template<class... Args>
  constexpr explicit expected(unexpect_t, Args&&...);
  template<class U, class... Args>
  constexpr explicit expected(unexpect_t, initializer_list<U>, Args&&...);
  // Destruktor
  constexpr ~expected();
  // Zuweisung
  constexpr expected& operator=(const expected&);
  constexpr expected& operator=(expected&&) noexcept(/* siehe Beschreibung */);
  template<class G>
  constexpr expected& operator=(const unexpected<G>&);
  template<class G>
  constexpr expected& operator=(unexpected<G>&&);
  constexpr void emplace() noexcept;
  // swap
  constexpr void swap(expected&) noexcept(/* siehe Beschreibung */);
  friend constexpr void swap(expected& x, expected& y) noexcept(noexcept(x.swap(y)));
  // Beobachter
  constexpr explicit operator bool() const noexcept;
  constexpr bool has_value() const noexcept;
  constexpr void operator*() const noexcept;
  constexpr void value() const&; // freestanding-deleted
  constexpr void value() &&;     // freestanding-deleted
  constexpr const E& error() const& noexcept;
  constexpr E& error() & noexcept;
  constexpr const E&& error() const&& noexcept;
  constexpr E&& error() && noexcept;
  template<class G = E>
  constexpr E error_or(G&&) const&;
  template<class G = E>
  constexpr E error_or(G&&) &&;
  // monadische Operationen
  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&&;
  // Gleichheitsoperatoren
  template<class T2, class E2>
    requires is_void_v<T2>
  friend constexpr bool operator==(const expected& x, const expected<T2, E2>& y);
  template<class E2>
  friend constexpr bool operator==(const expected&, const unexpected<E2>&);
private:
  bool /*has-val*/; // exposition-only
  union
  {
    E /*unex*/; // exposition-only
  };
};