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[英]Cannot infer lifetime for autoref when calling mutable method from closure
[英]Cannot infer appropriate lifetime for autoref when calling a method from an Iterator implementation
我正在嘗試為一個結構實現Iterator
特性,該結構充當i32
值數組的i32
,但我一直在編譯器中抱怨無法在下一個方法中推斷出生命周期。
我知道需要幫助理解迭代器的生命周期 ,但是因為我的結構只是借用了數組的一部分,所以我將實際元素的內存與我的IntegerArrayBag
分開。
#[derive(Debug)]
struct IntegerArrayBag<'a> {
arr: &'a [i32],
idx: usize,
}
impl<'a> IntegerArrayBag<'a> {
fn len(&self) -> usize {
self.arr.len()
}
fn get(&self, idx: usize) -> Option<&i32> {
if self.arr.len() > idx {
Some(&self.arr[idx])
} else {
None
}
}
}
impl<'a> Iterator for IntegerArrayBag<'a> {
type Item = &'a i32;
fn next(&mut self) -> Option<&'a i32> {
let idx = self.idx;
self.idx += 1;
self.get(idx)
}
}
如果我嘗試編譯此代碼 ,編譯器會抱怨:
error[E0495]: cannot infer an appropriate lifetime for autoref due to conflicting requirements
--> src/main.rs:27:14
|
27 | self.get(idx)
| ^^^
|
note: first, the lifetime cannot outlive the anonymous lifetime #1 defined on the method body at 24:5...
--> src/main.rs:24:5
|
24 | / fn next(&mut self) -> Option<&'a i32> {
25 | | let idx = self.idx;
26 | | self.idx += 1;
27 | | self.get(idx)
28 | | }
| |_____^
note: ...so that reference does not outlive borrowed content
--> src/main.rs:27:9
|
27 | self.get(idx)
| ^^^^
note: but, the lifetime must be valid for the lifetime 'a as defined on the impl at 21:1...
--> src/main.rs:21:1
|
21 | / impl<'a> Iterator for IntegerArrayBag<'a> {
22 | | type Item = &'a i32;
23 | |
24 | | fn next(&mut self) -> Option<&'a i32> {
... |
28 | | }
29 | | }
| |_^
note: ...so that expression is assignable (expected std::option::Option<&'a i32>, found std::option::Option<&i32>)
--> src/main.rs:27:9
|
27 | self.get(idx)
| ^^^^^^^^^^^^^
您需要更新get
方法以返回具有更長壽命的引用:
// Use 'a from impl<'a> IntegerArrayBag<'a>
fn get(&self, idx: usize) -> Option<&'a i32> {
然后它將編譯。
更改get(…)
以返回Option<&'a i32>
使其編譯。
游樂場網址: https : //play.rust-lang.org/?gist = 10783e90287b7111c126&version =stable
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