Code shared from the Rust Playground

playground.rs

use anyhow::Result;

// A function that returns a Result.
// We use 'anyhow::Result' as a shorthand for 'Result<T, anyhow::Error>'.
fn get_user_id(username: &str) -> Result<u32> {
    // This is a simple, illustrative error case.
    // We can use anyhow::bail! to create an immediate error.
    if username.is_empty() {
        // 'anyhow::bail!' is a macro that returns an error.
        anyhow::bail!("Username cannot be empty");
    }

    // A more realistic scenario might involve a database query or an API call
    // that returns an error. Here, we'll just simulate success.
    Ok(42) // Return a successful result with a value.
}

// The 'main' function must also return 'anyhow::Result<()>'.
// The '()' indicates that the function returns no value on success,
// only an error on failure.
fn main() -> Result<()> {
    // Call the function with a valid username.
    let user_id = get_user_id("alice")?;
    println!("Successfully retrieved user ID: {}", user_id);

    // Call the function with an invalid (empty) username.
    // The '?' operator will propagate the error, causing main to exit.
    let _user_id_empty = get_user_id("")?;

    // This line will never be reached because of the error above.
    println!("This line will not be printed.");

    // The '?' operator automatically returns the error from the function.
    // If the function completes without an error, we return 'Ok(())'.
    Ok(())
}