前回の続き

RUST勉強中、6/4の積み上げ

今回はthiserrorクレートを使用したエラーハンドリングです。

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

# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

[dependencies]
clap = { version = "3.1.6", features = ["derive"] }
anyhow = { version = "1.0" }
thiserror = { version = "1.0" }

use thiserror::Error;

#[derive(Error, Debug)]
enum MyError {
    #[error("failed to read string from {0}")]
    ReadError(String),
    #[error(transparent)]
    ParseError(#[from] std::num::ParseIntError),
}

fn get_int_from_file() -> Result<i32, MyError> {
    let path = "number.txt";

    let num_str = 
        std::fs::read_to_string(path).map_err(|_| MyError::ReadError(path.into()))?;

    num_str
        .trim()
        .parse::<i32>()
        .map(|t| t * 2)
        .map_err(MyError::from)
}

fn main() {
    match get_int_from_file() {
        Ok(x) => println!("{}", x),
        Err(e) => println!("{:#}", e),
    }
}