std::expected<T,E>:: emplace

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主模板
template < class ... Args > constexpr T & emplace ( Args && ... args ) noexcept ;	(1)	(自 C++23 起)
template < class U, class ... Args > constexpr T & emplace ( std:: initializer_list < U > il, Args && ... args ) noexcept ;	(2)	(自 C++23 起)
void 部分特化
constexpr void emplace ( ) noexcept ;	(3)	(自 C++23 起)

构造一个期望值的原位构造版本。调用后， has_value() 将返回 true。

1) 销毁所含值，随后使用 std:: forward < Args > ( args ) ... 对 * this 中所含期望值进行直接初始化。

此重载仅当 std:: is_nothrow_constructible_v < T, Args... > 为 true 时参与重载决议。

2) 销毁所含值，然后使用 il 和 std:: forward < Args > ( args ) ... 直接初始化 * this 中包含的期望值。

此重载仅当 std:: is_nothrow_constructible_v < T, std:: initializer_list < U > & , Args... > 为 true 时参与重载决议。

3) 若 * this 包含意外值，则销毁该值。

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Language
Standard library
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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
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Ranges library (C++20)
Algorithms library
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Member functions
expected::expected
expected::~expected
expected::operator=
Observers
expected::operator-> expected::operator*
expected::operator bool expected::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
Modifiers
expected::emplace
expected::swap
Non-member functions
operator== (std::expected)
swap (std::expected)
Helper classes
unexpected
bad_expected_access
unexpect_t unexpect

目录

args	-	传递给构造函数的参数
il	-	传递给构造函数的初始化列表