Question

我正在尝试编写一个派生serde::Deserialize的结构，但它也有一个应该派生serde::Deserialize的字段：

extern crate serde;
#[macro_use]
extern crate serde_derive;

use serde::{Deserialize, Serialize};

#[derive(PartialEq, Serialize, Deserialize)]
pub struct Record<'a, T>
where
    T: 'a + Serialize + Deserialize<'a>,
{
    id: &'a str,
    created_at: &'a str,
    created_by: Option<&'a str>,
    last_updated_at: Option<&'a str>,
    object: &'a T,
}

impl<'a, T> Record<'a, T>
where
    T: 'a + Serialize + Deserialize<'a>,
{
    pub fn new(
        id: &'a str,
        created_at: &'a str,
        created_by: Option<&'a str>,
        last_updated_at: Option<&'a str>,
        object: &'a T,
    ) -> Self {
        Record {
            id,
            created_at,
            created_by,
            last_updated_at,
            object,
        }
    }
}

fn main() {}

我一直在改变代码一段时间，但我无法将这个想法编译好。我现在得到的错误是：

error[E0283]: type annotations required: cannot resolve `T: serde::Deserialize<'a>`
 --> src/main.rs:7:32
  |
7 | #[derive(PartialEq, Serialize, Deserialize)]
  |                                ^^^^^^^^^^^
  |
  = note: required by `serde::Deserialize`

Answer 1

一般来说，you should not write Serde trait bounds on structs。

rustc --explain E0283解释了您的问题：

当编译器没有足够的信息来明确选择实现
时，会发生此错误

我发现使用#[serde(bound()]声明边界会使示例编译：

#[derive(PartialEq, Serialize, Deserialize)]
pub struct Record<'a, T: 'a> {
    id: &'a str,
    created_at: &'a str,
    created_by: Option<&'a str>,
    last_updated_at: Option<&'a str>,
    #[serde(bound(deserialize = "&'a T: Deserialize<'de>"))]
    object: &'a T,
}

作为另一种解决方案，由于T是通用的并且可能是参考，因此请考虑更改Record定义，以便Serde不需要更明确的指示：

#[derive(PartialEq, Serialize, Deserialize)]
pub struct Record<'a, T: 'a> {
    id: &'a str,
    created_at: &'a str,
    created_by: Option<&'a str>,
    last_updated_at: Option<&'a str>,
    object: T,
}

impl<'a, T: 'a> Record<'a, T> {
    pub fn new(
        id: &'a str,
        created_at: &'a str,
        created_by: Option<&'a str>,
        last_updated_at: Option<&'a str>,
        object: T,
    ) -> Self {
        Record {
            id,
            created_at,
            created_by,
            last_updated_at,
            object,
        }
    }
}

无法解析T：serde :: Deserialize＆lt;'a＆gt;何时在泛型结构上派生反序列化

1 个答案: