anyhow

Do flexible error handling with the anyhow crate.

anyhow

In applications, gathering errors from different sources into a single type is often enough. anyhow::Result<T> is shorthand for Result<T, anyhow::Error> and accepts any error type via ?:

// Cargo.toml: anyhow = "1"
use anyhow::{bail, Result};

fn oku(s: &str) -> Result<i32> {
    let n: i32 = s.trim().parse()?;
    if n == 0 {
        bail!("sıfır olamaz");
    }
    Ok(100 / n)
}

bail! returns Err immediately with a formatted message. Its closest standard library counterpart is Box<dyn Error>.

The same pattern with std

In the exercise we'll use the standard counterpart instead of anyhow; the structure is the same:

use std::error::Error;

fn oku(s: &str) -> Result<i32, Box<dyn Error>> {
    let n: i32 = s.trim().parse()?;       // ParseIntError → Box
    if n == 0 {
        return Err("sıfır olamaz".into()); // &str → Box
    }
    Ok(100 / n)
}

On top of this, anyhow offers adding context, printing the error chain and backtraces.

Exercise Flexible error type

Write the oku function above with Box<dyn Error>. For "4", "abc" and "0", print the result on success and hata: MESSAGE on error.

Show example solution

use std::error::Error;

fn oku(s: &str) -> Result<i32, Box<dyn Error>> {
    let n: i32 = s.trim().parse()?;
    if n == 0 {
        return Err("sıfır olamaz".into());
    }
    Ok(100 / n)
}

fn main() {
    for g in ["4", "abc", "0"] {
        match oku(g) {
            Ok(n) => println!("{}", n),
            Err(e) => println!("hata: {}", e),
        }
    }
}

Test yourself

How is a string converted into a <code>Box<dyn Error></code>?
- panic!("mesaj")
- "mesaj".into() or Box::from("mesaj")
- It can't be
- Error::new("mesaj")
Show answer

"mesaj".into() or Box::from("mesaj") — The standard library provides From<..> for Box<dyn Error> for &str and String.

Error from text

if n == 0 {
    return Err("sıfır olamaz".____());
}

Show answer

if n == 0 {
    return Err("sıfır olamaz".into());
}

Input and oku result

"4"

25
" 10 "

10
"abc"

invalid digit found in string
"0"

sıfır olamaz

Next lesson: Error conversion

We Are Enhancing Your Experience

Cookie Preferences

Strictly Necessary Cookies

Analytical Cookies