在一个涉及自定义 Serde (1.0) 序列化和反序列化方法的项目中，我依靠这个测试例程来检查序列化对象并返回是否会产生等效对象。
// let o: T = ...;
let buf: Vec<u8> = to_vec(&o).unwrap();
let o2: T = from_slice(&buf).unwrap();
assert_eq!(o, o2);
这样做内联效果很好。我迈向可重用性的下一步是check_serde为此目的创建一个函数。
pub fn check_serde<T>(o: T)
where
T: Debug + PartialEq<T> + Serialize + DeserializeOwned,
{
let buf: Vec<u8> = to_vec(&o).unwrap();
let o2: T = from_slice(&buf).unwrap();
assert_eq!(o, o2);
}
这适用于拥有类型，但不适用于具有生命周期边界的类型（Playground）：
check_serde(5);
check_serde(vec![1, 2, 5]);
check_serde("five".to_string());
check_serde("wait"); // [E0279]
错误：
error[E0279]: the requirement `for<'de> 'de : ` is not satisfied (`expected bound lifetime parameter 'de, found concrete lifetime`)
--> src/main.rs:24:5
|
24 | check_serde("wait"); // [E0277]
| ^^^^^^^^^^^
|
= note: required because of the requirements on the impl of `for<'de> serde::Deserialize<'de>` for `&str`
= note: required because of the requirements on the impl of `serde::de::DeserializeOwned` for `&str`
= note: required by `check_serde`
由于我希望使函数适用于这些情况（包括带有字符串切片的结构），我尝试了一个具有显式对象反序列化生命周期的新版本：
pub fn check_serde<'a, T>(o: &'a T)
where
T: Debug + PartialEq<T> + Serialize + Deserialize<'a>,
{
let buf: Vec<u8> = to_vec(o).unwrap();
let o2: T = from_slice(&buf).unwrap();
assert_eq!(o, &o2);
}
check_serde(&5);
check_serde(&vec![1, 2, 5]);
check_serde(&"five".to_string());
check_serde(&"wait"); // [E0405]
此实现导致另一个问题，它不会编译（Playground）。
error[E0597]: `buf` does not live long enough
--> src/main.rs:14:29
|
14 | let o2: T = from_slice(&buf).unwrap();
| ^^^ does not live long enough
15 | assert_eq!(o, &o2);
16 | }
| - borrowed value only lives until here
|
note: borrowed value must be valid for the lifetime 'a as defined on the function body at 10:1...
--> src/main.rs:10:1
|
10 | / pub fn check_serde<'a, T>(o: &'a T)
11 | | where T: Debug + PartialEq<T> + Serialize + Deserialize<'a>
12 | | {
13 | | let buf: Vec<u8> = to_vec(o).unwrap();
14 | | let o2: T = from_slice(&buf).unwrap();
15 | | assert_eq!(o, &o2);
16 | | }
| |_^
我已经预料到了这一点：这个版本意味着序列化的内容（以及反序列化的对象）与输入对象一样长，这是不正确的。缓冲区只意味着与函数的作用域一样长。
我的第三次尝试试图构建原始输入的自有版本，从而避免了具有不同生命周期边界的反序列化对象的问题。该ToOwned特征似乎适合此用例。
pub fn check_serde<'a, T: ?Sized>(o: &'a T)
where
T: Debug + ToOwned + PartialEq<<T as ToOwned>::Owned> + Serialize,
<T as ToOwned>::Owned: Debug + DeserializeOwned,
{
let buf: Vec<u8> = to_vec(&o).unwrap();
let o2: T::Owned = from_slice(&buf).unwrap();
assert_eq!(o, &o2);
}
这使得该函数现在适用于纯字符串切片，但不适用于包含它们的复合对象（Playground）：
check_serde(&5);
check_serde(&vec![1, 2, 5]);
check_serde(&"five".to_string());
check_serde("wait");
check_serde(&("There's more!", 36)); // [E0279]
同样，我们偶然发现了与第一个版本相同的错误类型：
error[E0279]: the requirement `for<'de> 'de : ` is not satisfied (`expected bound lifetime parameter 'de, found concrete lifetime`)
--> src/main.rs:25:5
|
25 | check_serde(&("There's more!", 36)); // [E0279]
| ^^^^^^^^^^^
|
= note: required because of the requirements on the impl of `for<'de> serde::Deserialize<'de>` for `&str`
= note: required because of the requirements on the impl of `for<'de> serde::Deserialize<'de>` for `(&str, {integer})`
= note: required because of the requirements on the impl of `serde::de::DeserializeOwned` for `(&str, {integer})`
= note: required by `check_serde`
诚然，我不知所措。我们如何构建一个通用函数，使用 Serde 序列化一个对象并将其反序列化回一个新对象？特别是，这个功能可以在 Rust（稳定或夜间）中实现吗？如果可以，我的实现缺少哪些调整？