在使用泛型和生存期的同时,使用serde/serde_JSON对JSON序列化/反序列化进行Rust?

这个问题与 serde_json with deserialize and lifetimes for generic function 因为from_slice和from_str都不起作用,而且错误消息也不同。

这个问题与 serde/rust deserialize JSON into Hashmap ,因为他们不会遇到特质界限的问题。

这个问题与 Lifetime error with Serde in a Generic Function 因为当我将Deserialize更改为DeserializeOwned或实现更高级别的特征边界时,我仍然会遇到这个问题。

我的目标很简单:围绕一个范围映射(crate:rangemap)创建一个结构包装器(它已经可以使用serde1功能进行序列化),允许我将数据保存到一个文件中。

我还希望它在结构被丢弃时调用save函数(通过执行Drop) 为了简洁起见,以下代码缺少一些明显的检查(文件位置是否有效)。

结构定义:

    use serde::{Deserialize, Serialize};
    use serde_json;
    use rangemap::RangeMap;
    use serde::de::DeserializeOwned;
    #[derive(Debug, Clone, Serialize, Deserialize)]
    pub struct RangeDataStorage<K, V> 
        where
            K: Ord + Clone + Eq + Debug + Default + Serialize + Deserialize,
            V: Default + Serialize + Debug + Eq + Clone + Deserialize {
        range_map: RangeMap<K, V>,
    }

我已经对structimpls进行了几次迭代:

结构impl:

    impl<K, V> RangeDataStorage<K, V>
        where
            K: Ord + Clone + Eq + Debug + Default + Serialize + Deserialize,
            V: Default + Serialize + Debug + Eq + Clone + Deserialize{
        pub fn new(location: Option<String>) -> Result<RangeDataStorage<K, V>, Box<dyn Error>> {
            if location.is_some() {
                // load from file
                let location = location.unwrap();
                let data = std::fs::read_to_string(location)?;
                let data: RangeDataStorage<K, V> = serde_json::from_str(&data)?;
                let data = data.clone(); // does not fix problem
                return Ok(data);
            }
            Ok(
                RangeDataStorage {
                    range_map: RangeMap::new(),
                }
            )
        }
    
        pub fn insert(&mut self, key_start: K, key_end: K, value: V) {
            let range = Range {
                start: key_start,
                end: key_end,
            };
            self.range_map.insert(range, value);
        }
    
        pub fn save(&mut self, location: String) {
            let file = std::fs::File::create(location).unwrap();
            let writer = std::io::BufWriter::new(file);
            let res = serde_json::to_writer(writer, self);
            match res {
                Ok(_) => {},
                Err(e) => { println!("Error while saving file : {:?}", e); }
            }
        }
    
        pub fn get(&self, key: K) -> Option<&V> {
            self.range_map.get(&key)
        }
    }

货物投诉:

error[E0106]: missing lifetime specifier
  --> src\main.rs:13:61
   |
13 |         K: Ord + Clone + Eq + Debug + Default + Serialize + Deserialize,
   |                                                             ^^^^^^^^^^^ expected named lifetime parameter
   |
   = note: for more information on higher-ranked polymorphism, visit https://doc.rust-lang.org/nomicon/hrtb.html
help: consider making the bound lifetime-generic with a new `'a` lifetime
   |
13 |         K: Ord + Clone + Eq + Debug + Default + Serialize + for<'a> Deserialize<'a>,
   |                                                             +++++++            ++++
help: consider making the bound lifetime-generic with a new `'a` lifetime
   |
13 |         for<'a> K: Ord + Clone + Eq + Debug + Default + Serialize + Deserialize<'a>,
   |         +++++++                                                                ++++
help: consider introducing a named lifetime parameter
   |
11 ~ pub struct RangeDataStorage<'a, K, V>
12 |     where
13 ~         K: Ord + Clone + Eq + Debug + Default + Serialize + Deserialize<'a>,

在这个迭代中,cargo抱怨缺少生存期说明符。我仍然不确定为什么这是个问题。 我已经阅读了serde反序列化程序的终身文章:

https://serde.rs/lifetimes.html

我不确定我错过了什么。我认为生存期是必要的,因为serde专注于零副本反序列化(反序列化的对象指的是反序列化器借用的数据,因此借用检查器需要确保借用的数据不会超出范围,从而延长生存期)。

但是,克隆数据应该可以解决这个问题,对吧?事实并非如此。

Cargo建议为缺失的寿命说明符添加更高的等级特征边界;前面提到的serde文章提到,更高级别的特征边界相当于使用DeserializeOwned(我两者都尝试过):

添加更高等级的特征边界:

    #[derive(Debug, Clone, Serialize, Deserialize)]
    pub struct RangeDataStorage<K, V>
        where
            K: Ord + Clone + Eq + Debug + Default + Serialize + for<'a>Deserialize<'a>,
            V: Default + Serialize + Debug + Eq + Clone + for<'a>Deserialize<'a> {
        range_map: RangeMap<K, V>,
    }
    
    impl<K, V> RangeDataStorage<K, V>
        where
            K: Ord + Clone + Eq + Debug + Default + Serialize + for<'a>Deserialize<'a>,
            V: Default + Serialize + Debug + Eq + Clone + for<'a>Deserialize<'a>{

新问题,是否需要键入注释?哪里怎样

    error[E0283]: type annotations needed: cannot satisfy `K: Deserialize<'_>`
      --> src\main.rs:11:12
       |
    11 | pub struct RangeDataStorage<K, V>
       |            ^^^^^^^^^^^^^^^^^^^^^^
       |
    note: multiple `impl`s or `where` clauses satisfying `K: Deserialize<'_>` found
      --> src\main.rs:10:35
       |
    10 | #[derive(Debug, Clone, Serialize, Deserialize)]
       |                                   ^^^^^^^^^^^
    ...
    13 |         K: Ord + Clone + Eq + Debug + Default + Serialize + for<'a>Deserialize<'a>,
       |                                                             ^^^^^^^^^^^^^^^^^^^^^^
    note: required for `RangeDataStorage<K, V>` to implement `Deserialize<'de>`
      --> src\main.rs:10:35
       |
    10 | #[derive(Debug, Clone, Serialize, Deserialize)]
       |                                   ^^^^^^^^^^^ unsatisfied trait bound introduced in this `derive` macro
    11 | pub struct RangeDataStorage<K, V>
       |            ^^^^^^^^^^^^^^^^^^^^^^
       = note: this error originates in the derive macro `Deserialize` (in Nightly builds, run with -Z macro-backtrace for more info)

当用DeserializeOwned替换较高级别的特征边界时,也会出现同样的错误:

    #[derive(Debug, Clone, Serialize, Deserialize)]
    pub struct RangeDataStorage<K, V>
        where
            K: Ord + Clone + Eq + Debug + Default + Serialize + DeserializeOwned,
            V: Default + Serialize + Debug + Eq + Clone + DeserializeOwned {
        range_map: RangeMap<K, V>,
    }
    
    impl<K, V> RangeDataStorage<K, V>
        where
            K: Ord + Clone + Eq + Debug + Default + Serialize + DeserializeOwned,
            V: Default + Serialize + Debug + Eq + Clone + DeserializeOwned{

    error[E0283]: type annotations needed: cannot satisfy `K: Deserialize<'_>`
      --> src\main.rs:11:12
       |
    11 | pub struct RangeDataStorage<K, V>
       |            ^^^^^^^^^^^^^^^^^^^^^^
       |
    note: multiple `impl`s or `where` clauses satisfying `K: Deserialize<'_>` found
      --> src\main.rs:10:35
       |
    10 | #[derive(Debug, Clone, Serialize, Deserialize)]
       |                                   ^^^^^^^^^^^
    ...
    13 |         K: Ord + Clone + Eq + Debug + Default + Serialize + DeserializeOwned,
       |                                                             ^^^^^^^^^^^^^^^^
    note: required for `RangeDataStorage<K, V>` to implement `Deserialize<'de>`
      --> src\main.rs:10:35
       |
    10 | #[derive(Debug, Clone, Serialize, Deserialize)]
       |                                   ^^^^^^^^^^^ unsatisfied trait bound introduced in this `derive` macro
    11 | pub struct RangeDataStorage<K, V>
       |            ^^^^^^^^^^^^^^^^^^^^^^
       = note: this error originates in the derive macro `Deserialize` (in Nightly builds, run with -Z macro-backtrace for more info)

对这个问题进行简短的谷歌搜索会得到以下结果: https://github.com/serde-rs/serde/issues/2418

这对我没有帮助,因为删除结构上的where子句也会给我带来问题,因为货物现在抱怨类型K和V需要由Ord、Clone、Eq(反序列化所必需的)来约束。

在这一点上,我迷失了方向,我真的找不到任何关于相对简单的任务的信息,而且我甚至还没有实现Drop函数。

谢谢你能提供的任何帮助。