Experimental library header <experimental/optional>

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<experimental/execution>

Filesystem TS

<experimental/filesystem>

Parallelism TS (v1, v2)

`experimental/algorithm`
`experimental/execution_policy`
`experimental/exception_list`

`experimental/numeric`
`<experimental/simd>`
`experimental/task_block`

Library Fundamentals TS (v1, v2, v3)

`experimental/algorithm`
`<experimental/any>`
`experimental/array`
`experimental/chrono`
`experimental/deque`
`experimental/forward_list`
`<experimental/functional>`
`experimental/future`
`experimental/iterator`
`experimental/list`
`experimental/map`
`experimental/memory`
`<experimental/memory_resource>`
`experimental/numeric`
`<experimental/optional>`
`experimental/propagate_const`

`experimental/random`
`experimental/ratio`
`experimental/regex`
`experimental/scope`
`experimental/set`
`experimental/source_location`
`experimental/string`
`<experimental/string_view>`
`experimental/system_error`
`experimental/tuple`
`experimental/type_traits`
`experimental/unordered_map`
`experimental/unordered_set`
`experimental/utility`
`experimental/vector`

Concurrency TS

`experimental/atomic`
`experimental/barrier`

`experimental/future`
`experimental/latch`

Ranges TS

`<experimental/ranges/algorithm>`
`<experimental/ranges/concepts>`
`<experimental/ranges/functional>`
`<experimental/ranges/iterator>`

`<experimental/ranges/random>`
`<experimental/ranges/tuple>`
`<experimental/ranges/type_traits>`
`<experimental/ranges/utility>`

Coroutines TS


               experimental/coroutine

Networking TS

`experimental/buffer`
`experimental/executor`
`experimental/internet`
`experimental/io_context`

`<experimental/net>`
`experimental/netfwd`
`experimental/socket`
`experimental/timer`

Reflection TS

<experimental/reflect>

此头文件是 Library Fundamentals TS 的组成部分（ v1 ， v2 ）。

名称	描述
optional (library fundamentals TS)	可能持有或未持有对象的包装器 (类模板)
bad_optional_access (library fundamentals TS)	指示对不包含值的 optional 进行受检访问时引发的异常 (类)
in_place_t (library fundamentals TS)	用于 optional 类型原位构造的消歧标签类型 (类)
std::hash <std::experimental::optional>	特化 std::hash 算法 (类模板特化)
nullopt_t (library fundamentals TS)	未初始化状态 optional 类型的指示符 (类)

函数

比较操作
operator== operator!= operator< operator<= operator> operator>=	比较 `optional` 对象 (函数模板)
特化算法
std::swap (std::experimental::optional)	特化 std::swap 算法 (函数)
make_optional	创建 `optional` 对象 (函数模板)
哈希支持

概要

namespace std {
  namespace experimental {
  inline namespace fundamentals_v1 {
    // 5.4，对象类型的 optional
    template <class T> class optional;
    // 5.5，就地构造
    struct in_place_t{};
    constexpr in_place_t in_place{};
    // 5.6，未 engaged 状态指示器
    struct nullopt_t{见下文};
    constexpr nullopt_t nullopt(未指定);
    // 5.7，类 bad_optional_access
    class bad_optional_access;
    // 5.8，关系运算符
    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，与 nullopt 的比较
    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，与 T 的比较
    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!=

Compiler support
Freestanding and hosted
Language
Standard library
Standard library headers
Named requirements
Feature test macros (C++20)
Language support library
Concepts library (C++20)
Diagnostics library
Memory management library
Metaprogramming library (C++11)
General utilities library
Containers library
Iterators library
Ranges library (C++20)
Algorithms library
Strings library
Text processing library
Numerics library
Date and time library
Input/output library
Filesystem library (C++17)
Concurrency support library (C++11)
Execution control library (C++26)
Technical specifications
Symbols index
External libraries

cppreference.net

Namespaces

Variants

Experimental library header <experimental/optional>

目录

类

函数

比较操作

特化算法

哈希支持

概要