【Anyhow】错误向下转型

环境

• Time 2022-01-20
• Rust 1.58.0
• Anyhow 1.0.52

概念

参考：https://docs.rs/anyhow/latest/anyhow/

示例

toml

[package]
edition = "2021"
name = "game"
version = "0.1.0"

[dependencies]
anyhow = "*"
serde = {version = "*", features = ["derive"]}
serde_json = "*"

main.rs

use anyhow::Result;
use serde::Deserialize;

#[derive(Deserialize, Default)]
struct User {
    name: String,
    age: u8,
}

fn main() {
    let user = read_user();
    user.unwrap_or_else(|e| match e.downcast_ref::<std::io::Error>() {
        Some(e) => {
            println!("downcast error: {:?}", e.kind());
            User::default()
        }
        None => unreachable!(),
    });
}

fn read_user() -> Result<User> {
    let config = std::fs::read_to_string("user.json")?;
    let user: User = serde_json::from_str(&config)?;
    println!("name: {}, age: {}", user.name, user.age);
    Ok(user)
}

总结

可以对返回的错误进行向下转型，对不同的错误进行不同的处理。

附录