generics - Rust 和 serde 使用泛型反序列化

Question

我正在尝试使用泛型从文件中反序列化结构，以便与 Swagger 生成的 API 一起使用。所以我把这个几乎可以工作的东西拼凑在一起，但是我无法从“拥有”指针中解压外部结构对象，正如您在测试中看到的那样。

这可能是错误的策略，但问题是我有各种 yaml 文件，我想读入这些文件并反序列化以提示要反序列化为的正确结构。我不想为每个 Struct 实现一个“readfile”函数，因为有很多。所以我试图使这个通用库工作，它应该反序列化为正确的结构，并与 Swagger API 一起使用。

它非常接近工作，但我似乎无法打开 Outer<ExternalStructA>进入刚刚ExternalStructA .

Owned(ExternalStructA { x: 1, y: 2 })
Owned(ExternalStructB { a: 1, b: 2 })

lib.rs :

#[cfg(test)]
mod tests {
    use crate::generics_yaml_deserializer::Outer;
    use serde::{de, Deserialize, Deserializer, Serialize, Serializer};

    #[derive(Debug, Serialize, Deserialize)]
    pub struct ExternalStructA {
        x: u32,
        y: u32,
    }

    #[derive(Debug, Serialize, Deserialize)]
    pub struct ExternalStructB {
        a: u64,
        b: u64,
    }

    #[test]
    fn deserialize() {
        let a = r#"---
ptr:
  x: 1
  y: 2
     "#;

        let b = r#"---
ptr:
  a: 1
  b: 2
        "#;

        let resulta: Outer<ExternalStructA> = serde_yaml::from_str(a).unwrap();
        assert_eq!(1, resulta.ptr.x); // I can't seem to get into ptr ExternalStructA
        let resultb: Outer<ExternalStructB> = serde_yaml::from_str(b).unwrap();
        assert_eq!(1, resultb.ptr.a); // I can't seem to get into ptr ExternalStructB 
    }
}

mod generics_yaml_deserializer {
    use serde::{de, Deserialize, Deserializer, Serialize, Serializer};
    use std::error::Error;

    // empty holding struct which owns a owned ptr
    #[derive(Deserialize, Debug)]
    pub struct Outer<'a, T: 'a + ?Sized> {
        #[serde(bound(deserialize = "Ptr<'a, T>: Deserialize<'de>"))]
        pub ptr: Ptr<'a, T>,
    }

    #[derive(Debug)]
    pub enum Ptr<'a, T: 'a + ?Sized> {
        Ref(&'a T),
        Owned(Box<T>),
    }

    impl<'de, 'a, T: 'a + ?Sized> Deserialize<'de> for Ptr<'a, T>
    where
        Box<T>: Deserialize<'de>,
    {
        fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
            where
                D: Deserializer<'de>,
        {
            Deserialize::deserialize(deserializer).map(Ptr::Owned)
        }
    }
}

cargo 依赖:

serde = { version = "1.0", features = ["derive"] }
serde_derive = "1.0"
serde_yaml = "0.7.5"
serde_json = "1.0"

更新:

我已经部分成功地推出了 Struct:

let resulta: Outer<ExternalStructA> = serde_yaml::from_str(a).unwrap();
    match resulta.ptr {
        Ptr::Owned(e) => {assert_eq!(1, e.x);},
        Ptr::Ref(e) => {println!("error")},
        Ptr::Owned(_) => {println!("error")}
    };
}

但是当我尝试使用通用类型将其实现为一个函数时，我遇到了很多错误，主要是:

the trait `for<'de> tests::_IMPL_DESERIALIZE_FOR_ExternalStructA::_serde::Deserialize<'de>` is not implemented for `T`

非工作代码添加到 mod generics_yaml_deserializer

fn readfile<T>(filename: String) -> Result<Box<T>, Box<std::error::Error>> {
    let f = std::fs::File::open(filename)?;
    let config_data: Outer<T> = serde_yaml::from_reader(f)?;
    Ok(Box::new(config_data))
}

fn readconfig<T>(filename: String) -> Result<Box<T>, &'static str> {
    // read the config file
    let config_data = readfile(filename);
    match config_data {
        Ok(e) => {
            Ok(Box::new(e))
        },
        Err(_) => {
            Err("nadda")
        }
    }
}

Answer 1

只需声明T 是DeserializeOwned:

fn readfile<T: de::DeserializeOwned>(filename: String) -> Result<Box<T>, Box<std::error::Error>> {
    let f = std::fs::File::open(filename)?;
    let config_data: Outer<T> = serde_yaml::from_reader(f)?;
    match config_data.ptr {
        Ptr::Owned(data) => Ok(data),
        _ => unimplemented!(),
    }
}

与readconfig相同