问题

I'm here to help with the translation. Here's the translated code portion:

我正在尝试实现 serde 的 [serialize_with ](https://serde.rs/field-attrs.html) 属性。

我有以下代码：

```rust
use serde::Serializer;

pub fn serialize_json_as_string<S>(json: &serde_json::value::Value, s: S) -> Result<S::Ok, S::Error>
where
    S: Serializer,
{
    let string = serde_json::to_string(json).unwrap();
    s.serialize_str(&string)
}

我不喜欢倒数第二行的 unwrap()。但我无法弄清如何将 to_string 返回的错误转换为 S::Error。

我尝试用类似以下的代码替换 let 行：

let string = serde_json::to_string(json)?;

我得到了以下错误：

error[E0277]: `?` 无法将错误转换为 `<S as serde::Serializer>::Error`
  --> src/model/field_type.rs:30:45
   |
26 | pub fn serialize_json_as_string<S>(json: &serde_json::value::Value, s: S) -> Result<S::Ok, S::Error>
   |                                                                              ----------------------- 预期是 `<S as serde::Serializer>::Error` 因为这个原因
...
30 |     let string = serde_json::to_string(json)?;
   |                                             ^ 问题号操作 (`?`) 隐式地使用 `From` 特性对错误值执行转换
   | 注意：为了实现 `Result<<S as serde::Serializer>::Ok, <S as serde::Serializer>::Error>`，需要执行 `FromResidual<Result<Infallible, serde_json::Error>>`
help: 考虑进一步限制关联类型
   |
28 |     S: Serializer, <S as serde::Serializer>::Error: From<serde_json::Error>
   |                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

有关此错误的更多信息，请尝试 `rustc --explain E0277`。

还尝试将整个内容替换为以下代码：

match serde_json::to_string(json) {
   Ok(string) => s.serialize_str(&string),
   Err(e) => Err(e.into()),
}

类似的错误：

error[E0277]: 没有满足 `<S as serde::Serializer>::Error: From<serde_json::Error>` 的特性约束
  --> src/model/field_type.rs:32:25
   |
32 |         Err(e) => Err(e.into()),
   |                         ^^^^ 没有为 `<S as serde::Serializer>::Error` 实现 `From<serde_json::Error>` 的特性
   |
   = 注意：为了使 `serde_json::Error` 实现 `Into<<S as serde::Serializer>::Error>` 需要的特性约束
help: 考虑进一步限制关联类型
   |
28 |     S: Serializer, <S as serde::Serializer>::Error: From<serde_json::Error>
   |                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

有关此错误的更多信息，请尝试 `rustc --explain E0277`。

由于我不拥有 Serde，我假设我无法实现 into，因此我需要某种手动转换。我无法弄清楚它的具体实现方式。

<details>
<summary>英文:</summary>

I&#39;m trying to implement serde&#39;s [serialize_with ](https://serde.rs/field-attrs.html) attribute.

I have this code:

```rust
use serde::Serializer;

pub fn serialize_json_as_string&lt;S&gt;(json: &amp;serde_json::value::Value, s: S) -&gt; Result&lt;S::Ok, S::Error&gt;
where
    S: Serializer,
{
    let string = serde_json::to_string(json).unwrap();
    s.serialize_str(&amp;string)
}

I don't like the unwrap() on the second to last line. But I can't figure out how to convert the error that to_string returns into S::Error.

I've tried replacing the let line with something like:

let string = serde_json::to_string(json)?;

And I got:

error[E0277]: `?` couldn't convert the error to `<S as serde::Serializer>::Error`
  --> src/model/field_type.rs:30:45
   |
26 | pub fn serialize_json_as_string<S>(json: &serde_json::value::Value, s: S) -> Result<S::Ok, S::Error>
   |                                                                              ----------------------- expected `<S as serde::Serializer>::Error` because of this
...
30 |     let string = serde_json::to_string(json)?;
   |                                             ^ the trait `From<serde_json::Error>` is not implemented for `<S as serde::Serializer>::Error`
   |
   = note: the question mark operation (`?`) implicitly performs a conversion on the error value using the `From` trait
   = note: required for `Result<<S as serde::Serializer>::Ok, <S as serde::Serializer>::Error>` to implement `FromResidual<Result<Infallible, serde_json::Error>>`
help: consider further restricting the associated type
   |
28 |     S: Serializer, <S as serde::Serializer>::Error: From<serde_json::Error>
   |                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

For more information about this error, try `rustc --explain E0277`.

And also tried replacing the whole thing with:

match serde_json::to_string(json) {
   Ok(string) => s.serialize_str(&string),
   Err(e) => Err(e.into()),
}

Similar error:

error[E0277]: the trait bound `<S as serde::Serializer>::Error: From<serde_json::Error>` is not satisfied
  --> src/model/field_type.rs:32:25
   |
32 |         Err(e) => Err(e.into()),
   |                         ^^^^ the trait `From<serde_json::Error>` is not implemented for `<S as serde::Serializer>::Error`
   |
   = note: required for `serde_json::Error` to implement `Into<<S as serde::Serializer>::Error>`
help: consider further restricting the associated type
   |
28 |     S: Serializer, <S as serde::Serializer>::Error: From<serde_json::Error>
   |                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

For more information about this error, try `rustc --explain E0277`.

Since I don't own Serde, I assume I can't implement into, so I need some kind of manual conversion. I couldn't figure out what that would look like.

答案1

得分: 6

The error is not a serde error, but you can wrap it in a serde custom error like so:

use serde::{Serializer, ser::Error};

pub fn serialize_json_as_string<S>(json: &serde_json::value::Value, s: S) -> Result<S::Ok, S::Error>
where
    S: Serializer,
{
    let string = serde_json::to_string(json).map_err(S::Error::custom)?;
    s.serialize_str(&string)
}

Note that you need to import serde::ser::Error as that's the trait where the custom function comes from.

use serde::{Serializer, ser::Error};

pub fn serialize_json_as_string<S>(json: &serde_json::value::Value, s: S) -> Result<S::Ok, S::Error>
where
    S: Serializer,
{
    let string = serde_json::to_string(json).map_err(S::Error::custom)?;
    s.serialize_str(&string)
}