為不同包中的型別實現 Serialize 和 Deserialize

Rust 的一致性規則要求你實現特徵的特徵或型別必須在與 impl 相同的包中定義，因此不可能直接對不同包中的型別實現序列化和反序列化。該 NEWTYPE 模式和 Deref 脅迫提供了一種方法來實現序列化和反序列化該行為的方式為你愛的人同一個型別。

use serde::{Serialize, Serializer, Deserialize, Deserializer};
use std::ops::Deref;

// Pretend this module is from some other crate.
mod not_my_crate {
    pub struct Data { /* ... */ }
}

// This single-element tuple struct is called a newtype struct.
struct Data(not_my_crate::Data);

impl Serialize for Data {
    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
        where S: Serializer
    {
        // Any implementation of Serialize.
    }
}

impl Deserialize for Data {
    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
        where D: Deserializer
    {
        // Any implementation of Deserialize.
    }
}

// Enable `Deref` coercion.
impl Deref for Data {
    type Target = not_my_crate::Data;
    fn deref(&self) -> &Self::Target {
        &self.0
    }
}

// Now `Data` can be used in ways that require it to implement
// Serialize and Deserialize.
#[derive(Serialize, Deserialize)]
struct Outer {
    id: u64,
    name: String,
    data: Data,
}