我有一些代码并且它可以工作,但AFAIK借用是专门为避免像split_text
方法那样手动传入和传出方法。
fn main() {
println!("Hello, world!");
let mut test = String::from("12345");
let mut obj1 = Object {
text: test.as_mut_str(),
next: None,
};
for i in 0..5 {
obj1 = obj1.split_text(4 - i);
if let Some(obj) = obj1.next.as_ref() {
println!("{}", obj.text);
}
}
}
struct Object<'a> {
text: &'a mut str,
next: Option<Box<Object<'a>>>,
}
impl<'a> Object<'a> {
fn split_text(mut self, count: usize) -> Self {
let tmp = self.text;
let (part1, part2) = tmp.split_at_mut(count);
self.text = part1;
let obj2 = Object {
text: part2,
next: None,
};
self.next = Some(Box::new(obj2));
self
}
}
(Qazxswpoi)
但我无法弄清楚如何通过借阅检查
Playground
导致错误
impl<'a> Object<'a> {
fn split_text(&'a mut self, count: usize) {
let tmp = &mut self.text;
let (part1, part2) = tmp.split_at_mut(count);
self.text = part1;
let obj2 = Object {
text: part2,
next: None,
};
self.next = Some(Box::new(obj2));
}
}
(Qazxswpoi)
有没有办法使这个代码工作?
问题是你在error[E0499]: cannot borrow `obj1` as mutable more than once at a time
--> src/main.rs:11:9
|
11 | obj1.split_text(4 - i);
| ^^^^ mutable borrow starts here in previous iteration of loop
error[E0502]: cannot borrow `obj1.next` as immutable because it is also borrowed as mutable
--> src/main.rs:12:28
|
11 | obj1.split_text(4 - i);
| ---- mutable borrow occurs here
12 | if let Some(obj) = obj1.next.as_ref() {
| ^^^^^^^^^
| |
| immutable borrow occurs here
| mutable borrow later used here
error[E0506]: cannot assign to `self.text` because it is borrowed
--> src/main.rs:27:9
|
23 | impl <'a> Object<'a> {
| -- lifetime `'a` defined here
24 | fn split_text(&'a mut self, count:usize) {
25 | let tmp = &mut self.text;
| -------------- borrow of `self.text` occurs here
26 | let (part1, part2) = tmp.split_at_mut(count);
| ----------------------- argument requires that `self.text` is borrowed for `'a`
27 | self.text = part1;
| ^^^^^^^^^^^^^^^^^ assignment to borrowed `self.text` occurs here
函数中借用Playground可变对象obj1
生命周期,直到split_text
函数的末尾。
'a
你想为main
函数可变地借用它,即不同的(较小的)生命周期 - 你可以忽略或指定另一个 - 比如说fn main() {
println!("Hello, world!");
let mut test = String::from("12345");
let mut obj1 = Object { // 'a start
text: test.as_mut_str(),
next: None,
};
for i in 0..5 {
obj1 = obj1.split_text(4 - i); // borrow for 'a lifetime,
// Won't work in next iteration
if let Some(obj) = obj1.next.as_ref() { // Won't work
println!("{}", obj.text);
}
}
} // 'a end
。
split_text
明确的不同生命期版本(仅为完整性):
'b
此外,只有在需要时才能制作可变的东西。我改变了可变切片并分裂成正常。