英文:
What can be an owner?
问题
Rust book 中指出：
> Rust 中的每个值都有一个 所有者
它没有解释这个所有者是什么类型的实体。它是程序员吗？一个变量？一个语句？一个代码块？
"值所有者" 可以是什么类型的实体的确切定义是什么？
英文:
The Rust book states:
>Each value in Rust has an owner
It does not explain what type of entity this owner is. Is it a programmer? a variable? A statement? A code block?
What is the precise definition of what type of entity can be a 'value owner'?
答案1
得分: 1
通常，所有者是变量或字段；它们负责释放所拥有的值。然而，更令人惊讶的是，甚至程序二进制代码也可以是一个所有者。例如，这对于字符串字面值来说就是这种情况：
let s = "Hello World";
上面的字符串字面值存储在程序二进制代码中，s只是对它的引用。因此，它的生命周期是'static'，也就是字面值的寿命与程序执行相对应。
英文:
Usually, owners are variables or fields; they are responsible for dropping the value owned. However, more surprisingly, even the program binary can be an owner too. As an example, that's the case for string literals:
let s = "Hello World";
The string literal above is stored in the program binary itself, s is just a reference to it. As such, its lifetime is 'static, i.e., the literal lifespan corresponds to the program execution.
答案2
得分: 1
如其他人所述，所有者是变量或字段。
我只想添加一个实际示例：
fn main() {
// s 拥有这个字符串。
let s: String = String::from("Hello!");
// r 拥有引用，该引用又引用了 s。
// 它可以访问字符串，但不拥有它。
let r: &String = &s;
// 这意味着如果我们放弃 `s`，它拥有字符串，字符串将被销毁。
drop(s);
// 这意味着 `r` 现在也被强制放弃，因为它不拥有字符串，现在它会成为悬空引用。
借用检查器会阻止悬空引用，因此这会导致编译错误。
println!("{}", r);
}
error[E0505]: 无法从 `s` 中移出，因为它被借用
--> src/main.rs:10:10
|
7 | let r: &String = &s;
| -- 在这里对 `s` 进行了借用
...
10 | drop(s);
| ^ 在这里发生了 `s` 的移出
...
15 | println!("{}", r);
| - 后来在这里使用了借用
英文:
As other people stated, owners are variables or fields.
I just wanted to add a practical example:
fn main() {
// s is the owner of the string.
let s: String = String::from("Hello!");
// r is the owner of the reference, which in turn references s.
// It can access the string, but does not own it.
let r: &String = &s;
// That means if we drop `s`, which owns the string, the string gets destroyed.
drop(s);
// Meaning `r` is now also forced to be dropped, because it does not own the
// string, and would now be a dangling reference. The borrow checker prevents
// dangling references, so this is a compilation error.
println!("{}", r);
}
error[E0505]: cannot move out of `s` because it is borrowed
--> src/main.rs:10:10
|
7 | let r: &String = &s;
| -- borrow of `s` occurs here
...
10 | drop(s);
| ^ move out of `s` occurs here
...
15 | println!("{}", r);
| - borrow later used here
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