swap(std::expected)

 

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std::expected

成員函式

expected::expected

expected::~expected

expected::operator=

觀察器

expected::operator->expected::operator*

expected::operator boolexpected::has_value

expected::value

expected::error

expected::value_or

expected::error_or

Monadic operations

expected::and_then

expected::or_else

expected::transform

expected::transform_error

修改器

expected::emplace

expected::swap

非成員函式

operator==(std::expected)

swap(std::expected)

輔助類

unexpected

bad_expected_access

unexpect_tunexpect

 

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

過載 std::swap 演算法，用於 std::expected。交換 lhs 和 rhs 的狀態。有效地呼叫 lhs.swap(rhs)。

此過載僅在 lhs.swap(rhs) 有效時才參與過載決議。

此函式對於普通的非限定查詢或限定查詢不可見，並且僅當 std::expected<T, E> 是引數的關聯類時，才能透過實參依賴查詢找到。

引數

lhs, rhs

-

要交換狀態的 expected 物件

返回值

(無)

異常

noexcept 規範：  

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

示例

執行此程式碼

#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';
}

輸出

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

參閱

swap	交換內容 (公共成員函式)