std::ranges::destroy

 

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在标头 <memory> 定义
调用签名
template< no-throw-input-iterator I, no-throw-sentinel-for<I> S >     requires std::destructible<std::iter_value_t<I>> constexpr I destroy( I first, S last ) noexcept;	(1)	(C++20 起)
template< no-throw-input-range R >     requires std::destructible<ranges::range_value_t<R>> constexpr ranges::borrowed_iterator_t<R> destroy( R&& r ) noexcept;	(2)	(C++20 起)

1) 销毁范围 [first, last) 中的对象，如同用

for (; first != last; ++first)
    std::ranges::destroy_at(std::addressof(*first));
return first;

2) 同 (1)，但以 r 为源范围，如同以 ranges::begin(r) 为 first 并以 ranges::end(r) 为 last。

此页面上描述的函数式实体是 niebloid，即：

• 调用它们中的任何一个时不能显式指定模板实参。
• 它们都不对实参依赖查找可见。
• 在通过函数调用运算符左侧的名字进行无限定查找，找到它们之一时，禁止实参依赖查找。

实践中，可以作为函数对象，或者用某些特殊编译器扩展实现它们。

参数

first, last	-	代表要销毁的范围的迭代器-哨位对
r	-	要销毁的范围

返回值

比较等于 last 的迭代器。

复杂度

与 first 和 last 间的距离成线性。

可能的实现

struct destroy_fn { template<no-throw-input-iterator I, no-throw-sentinel-for<I> S> requires std::destructible<std::iter_value_t<I>> constexpr I operator()(I first, S last) const noexcept { for (; first != last; ++first) std::ranges::destroy_at(std::addressof(*first)); return first; }   template<no-throw-input-range R> requires std::destructible<std::ranges::range_value_t<R>> constexpr std::ranges::borrowed_iterator_t<R> operator()(R&& r) const noexcept { return operator()(std::ranges::begin(r), std::ranges::end(r)); } };   inline constexpr destroy_fn destroy{};

示例

下列示例演示如何用 ranges::destroy 销毁元素的相接序列。

运行此代码

#include <iostream>
#include <memory>
#include <new>
 
struct Tracer
{
    int value;
    ~Tracer() { std::cout << value << " 已析构\n"; }
};
 
int main()
{
    alignas(Tracer) unsigned char buffer[sizeof(Tracer) * 8];
 
    for (int i = 0; i < 8; ++i)
        new(buffer + sizeof(Tracer) * i) Tracer{i}; // 手工构造对象
 
    auto ptr = std::launder(reinterpret_cast<Tracer*>(buffer));
 
    std::ranges::destroy(ptr, ptr + 8);
}

输出：

0 已析构
1 已析构
2 已析构
3 已析构
4 已析构
5 已析构
6 已析构
7 已析构

参阅

ranges::destroy_n (C++20)	销毁范围中一定量的元素 (niebloid)
ranges::destroy_at (C++20)	销毁位于给定地址的元素 (niebloid)
destroy (C++17)	销毁一个范围中的对象 (函数模板)