为什么 Serde 不能为仅包含 &Path 的结构派生 Deserialize? [英] Why can Serde not derive Deserialize for a struct containing only a &Path?

问题描述

我尝试为包含对 Path 的引用的结构派生 serde::Deserialize.这产生了一条错误消息，如果您将 &'a Path 替换为 &'a str，则不会出现该错误消息.什么导致#[derive(Deserialize)]的不同行为?

I tried to derive serde::Deserialize for a struct containing a reference to a Path. This yielded an error message which doesn't occur if you replace &'a Path with &'a str. What causes the different behaviours of #[derive(Deserialize)]?

游乐场>

#!/bin/cargo script
//! ```cargo
//! [dependencies]
//! serde_derive="1.0"
//! serde="1.0"
//! ```

extern crate serde_derive;

use serde_derive::*;

#[derive(Deserialize)]
struct A<'a> {
    a: &'a std::path::Path,
    //a: &'a str,
}

fn main() {}

error[E0495]: cannot infer an appropriate lifetime for lifetime parameter `'de` due to conflicting requirements
 --> src/main.rs:7:5
  |
7 |     a: &'a std::path::Path,
  |     ^
  |
note: first, the lifetime cannot outlive the lifetime 'de as defined on the impl at 5:10...
 --> src/main.rs:5:10
  |
5 | #[derive(Deserialize)]
  |          ^^^^^^^^^^^
  = note: ...so that the types are compatible:
          expected _IMPL_DESERIALIZE_FOR_A::_serde::de::SeqAccess<'_>
             found _IMPL_DESERIALIZE_FOR_A::_serde::de::SeqAccess<'de>
note: but, the lifetime must be valid for the lifetime 'a as defined on the impl at 6:10...
 --> src/main.rs:6:10
  |
6 | struct A<'a> {
  |          ^^
  = note: ...so that the types are compatible:
          expected _IMPL_DESERIALIZE_FOR_A::_serde::Deserialize<'_>
             found _IMPL_DESERIALIZE_FOR_A::_serde::Deserialize<'_>

error[E0495]: cannot infer an appropriate lifetime for lifetime parameter `'de` due to conflicting requirements
 --> src/main.rs:7:5
  |
7 |     a: &'a std::path::Path,
  |     ^
  |
note: first, the lifetime cannot outlive the lifetime 'de as defined on the impl at 5:10...
 --> src/main.rs:5:10
  |
5 | #[derive(Deserialize)]
  |          ^^^^^^^^^^^
  = note: ...so that the types are compatible:
          expected _IMPL_DESERIALIZE_FOR_A::_serde::de::MapAccess<'_>
             found _IMPL_DESERIALIZE_FOR_A::_serde::de::MapAccess<'de>
note: but, the lifetime must be valid for the lifetime 'a as defined on the impl at 6:10...
 --> src/main.rs:6:10
  |
6 | struct A<'a> {
  |          ^^
  = note: ...so that the types are compatible:
          expected _IMPL_DESERIALIZE_FOR_A::_serde::Deserialize<'_>
             found _IMPL_DESERIALIZE_FOR_A::_serde::Deserialize<'_>

奇怪的是，如果结构体包含两个字段 _a: &'a Path 和 _b: &'a str ，代码就会编译...此时我认为这是一个错误.

Strangely enough, the code compiles if the struct contains both fields _a: &'a Path and _b: &'a str... At this point I think this is a bug.

推荐答案

向字段添加属性:#[serde(borrow)].这将向 serde 表明它应该借用价值.除了 &str 和 &[u8] 之外，您必须为每个借用提供此属性.

Add an attribute to the field: #[serde(borrow)]. That will indicate to serde that it should be borrowing the value. You must provide this attribute for every borrow except for &str and &[u8].

来源:https://serde.rs/lifetimes.html#borrowing-data-in-a-derived-impl

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