Skip to main content
easyrust

Day 13: Santa's error handling rant

Santa found it a good opportunity to have a look to see what Blitzen has been doing all this time when he was tech lead.

Rolling up his sleeves, he ran a git diff command and began scrolling through the commits. His candy-cane-themed monitor reflected the code as his eyes narrowed like a debugger catching a null pointer. Then he froze, staring at the parse_row function.

"Blitzen," he barked, "what is this disaster? return &'static str for errors? Seriously?!"

Blitzen shrugged, sipping his oat milk latte. "MVP, Santa. Move fast, y'know?"

Santa slammed his mug of hot coffee down, marshmallows flying. "MVP? Last time you were in charge, you tried to rewrite grep and cat in Rust because you were 'bored'! And now you're telling me you can't handle proper error types? It takes five minutes! Do you want runtime panics for Christmas?!"

Bernard leaned in. "What if we use an enum? Variants for different errors, match on them later. Clean, ergonomic."

Santa's face lit up like Rudolph's nose. "Finally, a solution that doesn't make me want to refactor the North Pole. Bernard, you get an extra cookie ration this year. Blitzen? No oat lattes for a week."

Blitzen sighed. "Enum it is."

Your Mission

  • Create an enum called ParseError with a few variants:

    • NoName
    • NoGoodDeeds
    • NoBadDeeds
    • InvalidGoodDeeds
    • InvalidBadDeeds

  • When errors displayed, they should be human-readable:

    • ParseError::NoName should display as "Name field is missing"
    • ParseError::NoGoodDeeds should display as "Good deeds field is missing"
    • ParseError::NoBadDeeds should display as "Bad deeds field is missing"
    • ParseError::InvalidGoodDeeds should display as "Good deeds value is invalid"
    • ParseError::InvalidBadDeeds should display as "Bad deeds value is invalid"

  • Implement the std::error::Error trait for ParseError.

  • Update the parse_row function to return meaningful errors using the ParseError enum.

  • Make sure you return the correct error variant for each error condition.

  • Handle the cases where an item in a row is missing. e.g. Alice,,3 in this case, you should return an error with the NoGoodDeeds variant.

Hints

If you're stuck or need a starting point, here are some hints to help you along the way!

Click here to show hints.

  • The Error trait requires you to implement the Display and Debug traits for the custom error type.

  • Implement Debug by using the derive macro. e.g. #[derive(Debug)]

  • For Display you must implement manually. e.g.

      use std::fmt;

  impl fmt::Display for ParseError {
      fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
          match self {
              ParseError::NoName => write!(f, "No name found"),
              // other variants...
          }
      }
  }

  • Now that both traits are implemented, you can implement the Error trait.

    use std::error::Error;

impl Error for ParseError {}