◐ Shell
clean mode source ↗

Experimental library header <experimental/optional> - cppreference.com

From cppreference.com

This header is part of the Library Fundamentals TS (v1, v2).

Classes

Name Description

(library fundamentals TS)

 a wrapper that may or may not hold an object
(class template) [edit]

(library fundamentals TS)

 exception indicating checked access to an optional that doesn't contain a value
(class) [edit]

(library fundamentals TS)

 disambiguation tag type for in-place construction of optional types
(class) [edit]
specializes the std::hash algorithm
(class template specialization) [edit]

(library fundamentals TS)

 indicator of optional type with uninitialized state
(class) [edit]

Functions

Comparison
compares optional objects
(function template) [edit]
Specialized algorithms
specializes the std::swap algorithm
(function) [edit]
creates an optional object
(function template) [edit]
Hash support

Synopsis

namespace std {
  namespace experimental {
  inline namespace fundamentals_v1 {

    // 5.4, optional for object types
    template <class T> class optional;

    // 5.5, In-place construction
    struct in_place_t{};
    constexpr in_place_t in_place{};

    // 5.6, Disengaged state indicator
    struct nullopt_t{see below};
    constexpr nullopt_t nullopt(unspecified);

    // 5.7, Class bad_optional_access
    class bad_optional_access;

    // 5.8, Relational operators
    template <class T>
      constexpr bool operator==(const optional<T>&, const optional<T>&);
    template <class T>
      constexpr bool operator!=(const optional<T>&, const optional<T>&);
    template <class T>
      constexpr bool operator<(const optional<T>&, const optional<T>&);
    template <class T>
      constexpr bool operator>(const optional<T>&, const optional<T>&);
    template <class T>
      constexpr bool operator<=(const optional<T>&, const optional<T>&);
    template <class T>
      constexpr bool operator>=(const optional<T>&, const optional<T>&);

    // 5.9, Comparison with nullopt
    template <class T> constexpr bool operator==(const optional<T>&, nullopt_t) noexcept;
    template <class T> constexpr bool operator==(nullopt_t, const optional<T>&) noexcept;
    template <class T> constexpr bool operator!=(const optional<T>&, nullopt_t) noexcept;
    template <class T> constexpr bool operator!=(nullopt_t, const optional<T>&) noexcept;
    template <class T> constexpr bool operator<(const optional<T>&, nullopt_t) noexcept;
    template <class T> constexpr bool operator<(nullopt_t, const optional<T>&) noexcept;
    template <class T> constexpr bool operator<=(const optional<T>&, nullopt_t) noexcept;
    template <class T> constexpr bool operator<=(nullopt_t, const optional<T>&) noexcept;
    template <class T> constexpr bool operator>(const optional<T>&, nullopt_t) noexcept;
    template <class T> constexpr bool operator>(nullopt_t, const optional<T>&) noexcept;
    template <class T> constexpr bool operator>=(const optional<T>&, nullopt_t) noexcept;
    template <class T> constexpr bool operator>=(nullopt_t, const optional<T>&) noexcept;

    // 5.10, Comparison with T
    template <class T> constexpr bool operator==(const optional<T>&, const T&);
    template <class T> constexpr bool operator==(const T&, const optional<T>&);
    template <class T> constexpr bool operator!=(const optional<T>&, const T&);
    template <class T> constexpr bool operator!=(const T&, const optional<T>&);
    template <class T> constexpr bool operator<(const optional<T>&, const T&);
    template <class T> constexpr bool operator<(const T&, const optional<T>&);
    template <class T> constexpr bool operator<=(const optional<T>&, const T&);
    template <class T> constexpr bool operator<=(const T&, const optional<T>&);
    template <class T> constexpr bool operator>(const optional<T>&, const T&);
    template <class T> constexpr bool operator>(const T&, const optional<T>&);
    template <class T> constexpr bool operator>=(const optional<T>&, const T&);
    template <class T> constexpr bool operator>=(const T&, const optional<T>&);

    // 5.11, Specialized algorithms
    template <class T> void swap(optional<T>&, optional<T>&) noexcept(see below);
    template <class T> constexpr optional<see below> make_optional(T&&);

  } // namespace fundamentals_v1
  } // namespace experimental

  // 5.12, Hash support
  template <class T> struct hash;
  template <class T> struct hash<experimental::optional<T>>;

} // namespace std