不能将 `hsets` 借用为可变的,因为它也被借用为不可变的
cannot borrow `hsets` as mutable because it is also borrowed as immutable
想把HashSet[0]的元素移动到HashSet[1],但是总是遇到借用的错误:
我尝试使用 tmp vec 来保存元素,但问题仍然存在:
use std::collections::HashSet;
fn main() {
let mut hsets = vec![];
hsets.push(HashSet::new());
hsets[0].insert("a1");
hsets[0].insert("a2");
hsets.push(HashSet::new());
hsets[1].insert("b1");
hsets[1].insert("b2");
// tmp vec save hsets[0]: [a1, a2]
let mut arr = vec![];
for v in &hsets[0] {
arr.push(v);
}
for v2 in arr {
hsets[1].insert(v2);
}
}
结果:
error[E0502]: cannot borrow `hsets` as mutable because it is also borrowed as immutable
--> src/main.rs:18:9
|
13 | for v in &hsets[0] {
| ----- immutable borrow occurs here
...
17 | for v2 in arr {
| --- immutable borrow later used here
18 | hsets[1].insert(v2);
| ^^^^^ mutable borrow occurs here
error: aborting due to previous error
我假设您不想将 HashSet 移出 Vec 或取消分配它们,在这种情况下您可以这样做:
use std::collections::HashSet;
fn main() {
let mut hsets = vec![];
// first set
hsets.push(HashSet::new());
hsets[0].insert("a1");
hsets[0].insert("a2");
// second set
hsets.push(HashSet::new());
hsets[1].insert("b1");
hsets[1].insert("b2");
dbg!(&hsets);
assert_eq!(hsets[0].len(), 2);
assert_eq!(hsets[1].len(), 2);
// move elements from first set to second set
let (first, second) = hsets.split_at_mut(1);
second[0].extend(first[0].drain());
dbg!(&hsets);
assert_eq!(hsets[0].len(), 0);
assert_eq!(hsets[1].len(), 4);
}
如果您想更深入地了解为什么您的代码无法编译,请阅读 。
尝试像
一样明确 Vector 的类型
let mut arr: Vec<&str> = vec![]; // otherwise compiler is interpreting as Vec<&&str>
想把HashSet[0]的元素移动到HashSet[1],但是总是遇到借用的错误: 我尝试使用 tmp vec 来保存元素,但问题仍然存在:
use std::collections::HashSet;
fn main() {
let mut hsets = vec![];
hsets.push(HashSet::new());
hsets[0].insert("a1");
hsets[0].insert("a2");
hsets.push(HashSet::new());
hsets[1].insert("b1");
hsets[1].insert("b2");
// tmp vec save hsets[0]: [a1, a2]
let mut arr = vec![];
for v in &hsets[0] {
arr.push(v);
}
for v2 in arr {
hsets[1].insert(v2);
}
}
结果:
error[E0502]: cannot borrow `hsets` as mutable because it is also borrowed as immutable
--> src/main.rs:18:9
|
13 | for v in &hsets[0] {
| ----- immutable borrow occurs here
...
17 | for v2 in arr {
| --- immutable borrow later used here
18 | hsets[1].insert(v2);
| ^^^^^ mutable borrow occurs here
error: aborting due to previous error
我假设您不想将 HashSet 移出 Vec 或取消分配它们,在这种情况下您可以这样做:
use std::collections::HashSet;
fn main() {
let mut hsets = vec![];
// first set
hsets.push(HashSet::new());
hsets[0].insert("a1");
hsets[0].insert("a2");
// second set
hsets.push(HashSet::new());
hsets[1].insert("b1");
hsets[1].insert("b2");
dbg!(&hsets);
assert_eq!(hsets[0].len(), 2);
assert_eq!(hsets[1].len(), 2);
// move elements from first set to second set
let (first, second) = hsets.split_at_mut(1);
second[0].extend(first[0].drain());
dbg!(&hsets);
assert_eq!(hsets[0].len(), 0);
assert_eq!(hsets[1].len(), 4);
}
如果您想更深入地了解为什么您的代码无法编译,请阅读
尝试像
一样明确 Vector 的类型let mut arr: Vec<&str> = vec![]; // otherwise compiler is interpreting as Vec<&&str>