本文介绍了由于递归结构中的需求冲突,因此无法推断出适当的生存期的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!

问题描述

当我尝试编译此代码时:

When I try to compile this code:

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) }
    }
}

我收到此错误:

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) }
  |                               ^^^^^

为什么会这样?

推荐答案

这是因为您没有满足所需的义务.

This is because you haven't met the obligations that you require.

由于终身删除,您的代码等效于:

Due to lifetime elision, your code is equivalent to:

pub fn inside<'b>(outer: &'a mut Context<'b>) -> Context<'a>

将代码更改为

pub fn inside(outer: &'a mut Context<'a>) -> Context<'a>

它将编译.

这篇关于由于递归结构中的需求冲突,因此无法推断出适当的生存期的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持!

08-22 16:46
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