如何在闭包中正确定义生命周期

Question

impl Rate for Vec<VolumeRanged> {
    fn costs<'a, I>(&'a self, issues: &I, period: u32) -> Box<'a + Iterator<Item = f32>>
    where
        I: IntoIterator<Item=f32>,
        I::IntoIter: 'a
    {
        fn issue_cost(issue: f32, percentage: f32, constant: f32, max: f32) -> f32 {
            let r = issue * percentage / 100.0 + constant;
            match r.partial_cmp(&max) {
                Some(Less) => r,
                _ => max
            }
        }
        Box::new(issues.into_iter().map(|i| {
            let (pr, nr) = pairwise(self)
                        .find(|&(_, n)| in_range(&i, &n.range))
                        .expect("No range found");
            issue_cost(
                i,
                nr.percentage,
                pr.map_or(0.0, |x| x.max),
                nr.max,
            )
        }))
    }
}

锈在说

error[E0373]: closure may outlive the current function, but it borrows `self`, which is owned by the current function
  --> src/main.rs:43:41
   |
43 |         Box::new(issues.into_iter().map(|i| {
   |                                         ^^^ may outlive borrowed value `self`
44 |             let (pr, nr) = pairwise(self)
   |                                     ---- `self` is borrowed here
   |
help: to force the closure to take ownership of `self` (and any other referenced variables), use the `move` keyword
   |
43 |         Box::new(issues.into_iter().map(move |i| {
   |                                         ^

但我不想关闭所有权。我想要的是返回的盒装迭代器应该与self 和issues 一样长。他们一走，它就应该走。

我知道这可以通过将克隆的迭代器传递给 issues 而不是对它的引用来解决，我认为这里不需要它。

playground

Answer 1

将move 添加到闭包中。 self 具有 &Vec<VolumeRanged> 类型，因此闭包不会获得向量的所有权，它会捕获对向量的引用。