Error Propagation with the ? Operator

Snippet

Error Propagation with the ? Operator

The '?' operator is a concise way to handle errors. If a Result is an Err, it returns early from the function with that error; otherwise, it unwraps the Ok value.

snippet.rs
rust
use std::fs::File;
use std::io::{self, Read};
 
fn read_username() -> Result<String, io::Error> {
    let mut f = File::open("hello.txt")?;
    let mut s = String::new();
    f.read_to_string(&mut s)?;
    Ok(s)
}

Breakdown

File::open("hello.txt")?

Attempts to open a file. If it fails, the error is returned immediately.

Ok(s)

Wraps the successful result in an Ok variant.

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Error Propagation with the ? Operator

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