serde: 在Rust中反序列化`str`

huangapple
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英文:

serde: Deserialize `str` in Rust

问题

The error message indicates that the Deserialize trait is not implemented for str, but it is implemented for &'a str. To address this issue without modifying TypePath in main.rs, you can provide a custom implementation of Deserialize for Cou<'a, str> in the cou.rs file. Here's a potential solution:

  1. use serde::{Deserialize, Deserializer, Serialize};
  3. #[derive(Serialize)]
  4. pub enum Cou<'a, T>
  5. where
  6.     T: ToOwned + ?Sized,
  7. {
  8.     Borrowed(&'a T),
  9.     Upgraded(std::sync::Arc<T::Owned>),
  10. }
  12. impl<'de> Deserialize<'de> for Cou<'de, str> {
  13.     fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
  14.     where
  15.         D: Deserializer<'de>,
  16.     {
  17.         // Deserialize `&str` from the provided deserializer and create a `Cou::Borrowed`.
  18.         let s: &'de str = Deserialize::deserialize(deserializer)?;
  19.         Ok(Cou::Borrowed(s))
  20.     }
  21. }

This code provides a custom Deserialize implementation for Cou&lt;&#39;a, str&gt; by deserializing a &str and wrapping it in Cou::Borrowed. This way, you can handle the deserialization of str without modifying the main.rs code.

英文:

I am working on an existing codebase in Rust, wherein I need to serialize/deserialize a struct with a &lt;&#39;a, str&gt; type.

I am mentioning the minimal reproducible snippets here:

File: main.rs

  1. use serde::{Deserialize, Serialize};
  3. use crate::cou::Cou;
  5. #[derive(Debug, PartialEq, Eq, Hash, Clone, Serialize, Deserialize)]
  6. pub struct TypePath&lt;&#39;a&gt;(Vec&lt;Cou&lt;&#39;a, str&gt;&gt;);

File: cou.rs

  1. use std::{
  2.     borrow::Borrow,
  3.     sync::Arc,
  4. };
  6. use serde::{Deserialize, Serialize};
  8. #[derive(Serialize, Deserialize)]
  9. pub enum Cou&lt;&#39;a, T&gt;
  10. where
  11.     T: ToOwned + ?Sized,
  12. {
  13.     Borrowed(&amp;&#39;a T),
  14.     Upgraded(Arc&lt;T::Owned&gt;),
  15. }

When I build the above, it gives an error:

  1. error[E0277]: the trait bound `str: Deserialize&lt;&#39;_&gt;` is not satisfied
  2.    --&gt; src/ast.rs:136:25
  3.     |
  4. 136 | pub struct TypePath&lt;&#39;a&gt;(Vec&lt;Cou&lt;&#39;a, str&gt;&gt;);
  5.     |                         ^^^ the trait `Deserialize&lt;&#39;_&gt;` is not implemented for `str`
  6.     |
  7.     = help: the trait `Deserialize&lt;&#39;de&gt;` is implemented for `&amp;&#39;a str`
  8. note: required for `Cou&lt;&#39;a, str&gt;` to implement `Deserialize&lt;&#39;_&gt;`
  9.    --&gt; src/cou.rs:11:21
  10.     |
  11. 11  | #[derive(Serialize, Deserialize)]
  12.     |                     ^^^^^^^^^^^ unsatisfied trait bound introduced in this `derive` macro
  13. 12  | pub enum Cou&lt;&#39;a, T&gt;
  14.     |          ^^^^^^^^^^
  15.     = note: 1 redundant requirement hidden
  16.     = note: required for `Vec&lt;Cou&lt;&#39;a, str&gt;&gt;` to implement `Deserialize&lt;&#39;_&gt;`
  17.     = note: this error originates in the derive macro `Deserialize` (in Nightly builds, run with -Z macro-backtrace for more info)

Now the output says that the trait is implemented for &amp;&#39;a str but I do not want to change TypePath in main.rs as it is used widely in the remainder of the codebase. Is it possible to define Deserialize for str?

答案1

得分: 2

Cou与Cow具有相同的结构，因此您几乎可以从serde的实现中进行复制粘贴。

  1. use std::{sync::Arc};
  2. use std::borrow::Borrow;
  3. use std::ops::Deref;
  5. use serde::{Deserializer, Deserialize, Serializer, Serialize};
  7. pub enum Cou<'a, T>
  8.   where
  9.     T: ToOwned + ?Sized,
  10. {
  11.   Borrowed(&'a T),
  12.   Upgraded(Arc<T::Owned>),
  13. }
  16. impl<B: ?Sized + ToOwned> Deref for Cou<'_, B>
  17.   where
  18.     B::Owned: Borrow<B>,
  19. {
  20.   type Target = B;
  22.   fn deref(&self) -> &B {
  23.     match *self {
  24.       Cou::Borrowed(borrowed) => borrowed.borrow(),
  25.       Cou::Upgraded(ref owned) => owned.deref().borrow(),
  26.     }
  27.   }
  28. }
  31. impl<'a, T: ?Sized> Serialize for Cou<'a, T> where T: Serialize + ToOwned {
  32.   #[inline]
  33.   fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
  34.     where
  35.       S: Serializer,
  36.   {
  37.     (**self).serialize(serializer)
  38.   }
  39. }
  42. impl<'de, 'a, T: ?Sized> Deserialize<'de> for Cou<'a, T>
  43.   where
  44.     T: ToOwned,
  45.     T::Owned: Deserialize<'de>,
  46. {
  47.   #[inline]
  48.   fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
  49.     where
  50.       D: Deserializer<'de>,
  51.   {
  52.     T::Owned::deserialize(deserializer).map(Arc::new).map(Cou::Upgraded)
  53.   }
  54. }

Playground

英文:

Cou has the same structure as Cow, so you can almost copy-paste ser/de implementations from serde.

  1. use std::{sync::Arc};
  2. use std::borrow::Borrow;
  3. use std::ops::Deref;
  5. use serde::{Deserializer, Deserialize, Serializer, Serialize};
  7. pub enum Cou&lt;&#39;a, T&gt;
  8.   where
  9.     T: ToOwned + ?Sized,
  10. {
  11.   Borrowed(&amp;&#39;a T),
  12.   Upgraded(Arc&lt;T::Owned&gt;),
  13. }
  16. impl&lt;B: ?Sized + ToOwned&gt; Deref for Cou&lt;&#39;_, B&gt;
  17.   where
  18.     B::Owned: Borrow&lt;B&gt;,
  19. {
  20.   type Target = B;
  22.   fn deref(&amp;self) -&gt; &amp;B {
  23.     match *self {
  24.       Cou::Borrowed(borrowed) =&gt; borrowed.borrow(),
  25.       Cou::Upgraded(ref owned) =&gt; owned.deref().borrow(),
  26.     }
  27.   }
  28. }
  31. impl &lt;&#39;a, T: ?Sized&gt; Serialize for Cou&lt;&#39;a, T&gt; where T: Serialize + ToOwned {
  32.   #[inline]
  33.   fn serialize&lt;S&gt;(&amp;self, serializer: S) -&gt; Result&lt;S::Ok, S::Error&gt;
  34.     where
  35.       S: Serializer,
  36.   {
  37.     (**self).serialize(serializer)
  38.   }
  39. }
  42. impl&lt;&#39;de, &#39;a, T: ?Sized&gt; Deserialize&lt;&#39;de&gt; for Cou&lt;&#39;a, T&gt;
  43.   where
  44.     T: ToOwned,
  45.     T::Owned: Deserialize&lt;&#39;de&gt;,
  46. {
  47.   #[inline]
  48.   fn deserialize&lt;D&gt;(deserializer: D) -&gt; Result&lt;Self, D::Error&gt;
  49.     where
  50.       D: Deserializer&lt;&#39;de&gt;,
  51.   {
  52.     T::Owned::deserialize(deserializer).map(Arc::new).map(Cou::Upgraded)
  53.   }
  54. }

Playground

huangapple
  • 本文由 发表于 2023年5月13日 14:58:01
  • 转载请务必保留本文链接：https://go.coder-hub.com/76241465.html
  • rust
  • serde
  • serialization
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