swap(std::expected)

 

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std::expected

成员函数

expected::expected

expected::~expected

expected::operator=

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expected::value

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expected::transform

expected::transform_error

修改器

expected::emplace

expected::swap

非成员函数

operator==(std::expected)

swap(std::expected)

辅助类

unexpected

bad_expected_access

unexpect_tunexpect

 

friend constexpr void swap( expected& lhs, expected& rhs ) noexcept(/* 见下文 */);		(C++23 起)

为 std::expected 重载的 std::swap 算法。交换 lhs 与 rhs 的状态。等价于 lhs.swap(rhs)。

此重载只有在 lhs.swap(rhs) 合法时才会参与重载决议。

此函数对常规的无限定或有限定查找不可见，而只能在 std::expected<T, E> 为实参的关联类时由实参依赖查找找到。

参数

lhs, rhs

-

要交换状态的 expected 对象

返回值

（无）

异常

noexcept 说明：  

noexcept(noexcept(lhs.swap(rhs)))

示例

运行此代码

#include <expected>
#include <iostream>
#include <string>
 
using Ex = std::expected<std::string, int>;
 
void show(const Ex& ex1, const Ex& ex2)
{
    for (int i{}; i < 2; ++i)
    {
        std::cout << (i ? "ex2" : "ex1");
        if (const Ex& ex = (i ? ex2 : ex1); ex.has_value())
            std::cout << ".has_value() = " << *ex << '\n';
        else
            std::cout << ".error() = " << ex.error() << '\n';
    }
}
 
int main()
{
    Ex ex1("\N{DOG FACE}");
    Ex ex2{"\N{BONE}"};
    show(ex1, ex2);
    swap(ex1, ex2);
    std::cout << "swap(ex1, ex2);\n";
    show(ex1, ex2);
    std::cout << '\n';
 
    ex2 = std::unexpected(13);
    show(ex1, ex2);
    swap(ex1, ex2);
    std::cout << "swap(ex1, ex2);\n";
    show(ex1, ex2);
    std::cout << '\n';
 
    ex2 = std::unexpected(19937);
    show(ex1, ex2);
    swap(ex1, ex2);
    std::cout << "swap(ex1, ex2);\n";
    show(ex1, ex2);
    std::cout << '\n';
}

输出：

ex1.has_value() = 🐶
ex2.has_value() = 🦴
swap(ex1, ex2);
ex1.has_value() = 🦴
ex2.has_value() = 🐶
 
ex1.has_value() = 🦴
ex2.error() = 13
swap(ex1, ex2);
ex1.error() = 13
ex2.has_value() = 🦴
 
ex1.error() = 13
ex2.error() = 19937
swap(ex1, ex2);
ex1.error() = 19937
ex2.error() = 13

参阅

swap	交换内容 (公开成员函数)