mechanics.md

Mechanics

Error Handling

• Rust has a built in generic enum called Result.
• It allows us to return a value that has the possibility of failing.
• It is the idiomatic way in which the language does error handling.

enum Result<T,Q>{
    Ok(T),
    Err(Q)
}

Example:

fn might_fail(i:i32) -> Result<f32,String> {
    if i == 42 {
        Ok(13.0)
    } else {
        Err(String::from("this is not the right number"))   
    }
}

Verbose Way:

fn main() {
    let result = do_something_that_might_fail(12);
    match result {
        Ok(v) => println!("found {}", v),
        Err(e) => println!("Error: {}",e),
    }
}

Concise Way:

fn main() -> Result<(), String> {
    let v = do_something_that_might_fail(42)?;
    println!("found {}", v);
    Ok(())
}

Bad Way:

Don't use unwrap().

fn main() -> Result<(), String> {
    // concise but assumptive and gets ugly fast
    let v = do_something_that_might_fail(42)?;
    println!("found {}", v);
    
    // this will panic!
    let v = do_something_that_might_fail(1)?;
    println!("found {}", v);
    
    Ok(())
}

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