在循环内借用向量
我试图更新向量的每个元素，然后在每次迭代期间借用整个向量，例如：
#![allow(unused)]
#[derive(Debug)]
pub struct Foo {
value: i32,
}
fn main() {
let mut foos: Vec<Foo> = vec![Foo { value: 1 }, Foo { value: 2 }, Foo { value: 3 }];
for foo in &mut foos {
update_single(foo);
//save_all(&foos); <-- this doesn't compile - there's already a mutable borrow
}
}
fn update_single(foo: &mut Foo) {
println!("update_single");
foo.value *= foo.value;
}
fn save_all(foos: &Vec<Foo>) {
println!("save_all:");
for foo in foos {
println!("\t{:?}", foo);
}
}
注意：我将更新的向量保存为 blob，例如通过 serde_json。
I'm trying to update each element of a vector and then borrow the entire vector during each iteration, ex:
#![allow(unused)]
#[derive(Debug)]
pub struct Foo {
value: i32,
}
fn main() {
let mut foos: Vec<Foo> = vec![Foo { value: 1 }, Foo { value: 2 }, Foo { value: 3 }];
for foo in &mut foos {
update_single(foo);
//save_all(&foos); <-- this doesn't compile - there's already a mutable borrow
}
}
fn update_single(foo: &mut Foo) {
println!("update_single");
foo.value *= foo.value;
}
fn save_all(foos: &Vec<Foo>) {
println!("save_all:");
for foo in foos {
println!("\t{:?}", foo);
}
}
Note: I'm saving the updated vector as a blob e.g. via serde_json.
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评论（1）
for foo in &mut foos将在整个for循环中可变地借用整个foos。你可以可变地借用某样东西一次，也可以不可变地借用任意多次，但不能同时借用两者。因此，当您在循环期间可变地借用整个向量时，它不能再次被一成不变地借用，直到循环结束时释放该可变借用为止。
您可以通过仅在循环的一行上可变地借用每个元素来解决此问题，而不是借用整个循环的整个向量。
现在我们可变地获取数组中的每一项，并且它每次仅可变地借用该行。
for foo in &mut fooswill borrow the entirety offoosmutably throughout the entireforloop.You can either borrow something mutably once or immutably any number of times, but not both. So, when you borrow the entire vector mutably for the duration of the loop, it can't be immutably borrowed again until you let go of that mutable borrow when the loop finishes.
You can get around this by borrowing each element mutably only on one line of the loop, rather than borrowing the entire vector for the entire loop.
Now we mutably get each item in the array, and it only mutably borrows each time on that one line.