我想取向量的最后两个数字。为什么我不能逆转迭代器两次?
fn main() {
let double_reversed = &vec![1, 2, 3, 4, 5, 6, 7, 8, 9]
.into_iter()
.rev()
.take(2)
.rev()
.collect();
println!("{}", double_reversed); // expected 8, 9
}错误消息是:
error[E0277]: the trait bound `std::iter::Take<std::iter::Rev<std::vec::IntoIter<{integer}>>>: std::iter::DoubleEndedIterator` is not satisfied
--> src/main.rs:6:10
|
6 | .rev()
| ^^^ the trait `std::iter::DoubleEndedIterator` is not implemented for `std::iter::Take<std::iter::Rev<std::vec::IntoIter<{integer}>>>`
error[E0599]: no method named `collect` found for type `std::iter::Rev<std::iter::Take<std::iter::Rev<std::vec::IntoIter<{integer}>>>>` in the current scope
--> src/main.rs:7:10
|
7 | .collect();
| ^^^^^^^
|
= note: the method `collect` exists but the following trait bounds were not satisfied:
`std::iter::Rev<std::iter::Take<std::iter::Rev<std::vec::IntoIter<{integer}>>>> : std::iter::Iterator`
`&mut std::iter::Rev<std::iter::Take<std::iter::Rev<std::vec::IntoIter<{integer}>>>> : std::iter::Iterator`发布于 2018-12-16 00:55:22
正如编译器告诉您的(清理):
性状约束
Take<...>: DoubleEndedIterator不满意
只有在底层类型实现Iterator::Rev时才实现DoubleEndedIterator。
fn rev(self) -> Rev<Self>
where
Self: DoubleEndedIterator, Take不实现DoubleEndedIterator,因此不能在其上调用rev。
我就把它切成碎片:
let items = [1, 2, 3, 4, 5, 6, 7, 8, 9];
let last_2 = &items[items.len() - 2..];
assert_eq!(last_2, [8, 9]);https://stackoverflow.com/questions/53796779
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