[英]Cannot infer an appropriate lifetime due to conflicting requirements in a recursive struct
當我嘗試編譯此代碼時:
pub struct Context<'a> {
pub outer: Option<&'a mut Context<'a>>,
}
impl<'a> Context<'a> {
pub fn inside(outer: &'a mut Context) -> Context<'a> {
Context { outer: Some(outer) }
}
}
我收到這個錯誤:
error[E0495]: cannot infer an appropriate lifetime for lifetime parameter `'a` due to conflicting requirements
--> src/main.rs:7:9
|
7 | Context { outer: Some(outer) }
| ^^^^^^^
|
note: first, the lifetime cannot outlive the lifetime 'a as defined on the impl at 5:1...
--> src/main.rs:5:1
|
5 | / impl<'a> Context<'a> {
6 | | pub fn inside(outer: &'a mut Context) -> Context<'a> {
7 | | Context { outer: Some(outer) }
8 | | }
9 | | }
| |_^
note: ...so that expression is assignable (expected Context<'a>, found Context<'_>)
--> src/main.rs:7:9
|
7 | Context { outer: Some(outer) }
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
note: but, the lifetime must be valid for the anonymous lifetime #1 defined on the method body at 6:5...
--> src/main.rs:6:5
|
6 | / pub fn inside(outer: &'a mut Context) -> Context<'a> {
7 | | Context { outer: Some(outer) }
8 | | }
| |_____^
note: ...so that expression is assignable (expected &mut Context<'_>, found &mut Context<'_>)
--> src/main.rs:7:31
|
7 | Context { outer: Some(outer) }
| ^^^^^
為什么會這樣?
這是因為您沒有履行所需的義務。
由於終身省略,您的代碼相當於:
pub fn inside<'b>(outer: &'a mut Context<'b>) -> Context<'a>
將您的代碼更改為
pub fn inside(outer: &'a mut Context<'a>) -> Context<'a>
它會編譯。
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