Rust 如何获取Serde struct 的默认实例

发布于01月22日

让我们考虑以下示例代码(我的实际代码有十分之几的字段):

fn empty_field() -> Result<f64, String> {
    Err(String::new())
}

#[derive(Deserialize, Serialize)]
struct Record {
    #[serde(rename = "Apple", default)]
    a: f64,
    #[serde(rename = "Banana", default)]
    b: String,
    #[serde(rename = "Coconut", default = "empty_field")]
    c: Result<f64, String>,
}

是否可以获得基于Serde注释的默认实例，而无需手动定义，如下所示？

let empty_record = Record {
    a: 0.0,
    b: String::new(),
    c: Err(String::new()),
};

推荐答案

您可以直接从空的HashMap反序列化.

use serde::{
    de::value::{Error as SerdeError, MapDeserializer},
    Deserialize, Serialize,
}; // 1.0.193
use std::collections::HashMap;
use std::error::Error;

// your definitions here

fn main() -> Result<(), Box<dyn Error>> {
    let data = HashMap::<(), ()>::new(); // K, V types seem not to matter
    let record = Record::deserialize(MapDeserializer::<_, SerdeError>::new(data.into_iter()))?;
    println!("{record:?}");
    Ok(())
}