Day 5: Parsing naughty-list.csv

The elves stared at their screens. They had just written the Kid struct and were testing it with Santa’s data.

But something was wrong with the data, Prancer leaned back, smirking. "We forgot something obvious, didn’t we? The data’s raw strings—we need to parse it first."

Alice,10,2
Bob,5,5
Charlie,1,9

"We need to create another function," Prancer continued. "to parse the CSV rows into Kid structs."

Blitzen slammed his mug down. "And since Santa put me in charge of this project, I’m naming the function. It’s going to be called parse_row."

An elf from the back muttered just loud enough to hear, "Ugh, he thinks he’s better than us because Santa made him lead."

Blitzen shot them a look. "I heard that. If you’ve got a better name, I’m listening."

Silence.

"Exactly. parse_row it is."

The Frustration

Blitzen paced. "We need a function that takes a CSV row, splits it, and converts it into a Kid. Name is easy—it stays a String. The good and bad deeds, though, need to be parsed to u32."

"But what if the row has garbage data?" asked an elf, holding up a note with Charlie,,9 scribbled on it.

Prancer rolled his eyes. "Obviously, we handle errors. No .unwrap() shortcuts."

The Task

Blitzen wants you to create an associated function for the Kid struct and name it parse_row. It should take a CSV row as a &str and return a Result<Kid, &'static str>. The function should:

  • Split the CSV row into parts.
  • Extract the name as a String.
  • Parse the second and third fields as u32 for good and bad deeds.
  • Finally create a Kid struct using the new() associated function we created earlier.

Hints

If you're stuck, here are some hints to help guide you:

Click to show hints

  • Split the Row Use split(',') to divide the CSV row into parts. let fields = row.split(',');

  • Get Next Field Get the next field with next(), it's going to return an Option<&str>.

  • Must be mutable The next() method requires a mutable reference to the iterator. So make it mutable, let mut fields = row.split(',');.

  • Transform Option to Result Use ok_or(&str) to convert the Option to a Result. e.g., fields.next().ok_or("Missing field").

  • Propagate Errors (optional) Use ? to propagate errors. e.g., fields.next().ok_or("Missing field")?.

  • Create a String After you get access to the &str use the to_string() method to make it a String and have Ownership.

  • Parse Numbers Parse the second and third fields as u32 for good and bad deeds. Use .parse(), you can either turbofish parse::<u32>() or assign a type to the variable let good_deeds: u32 = fields.next().ok_or("Missing field")?.parse();.

  • Map the Error The error from the parse() method can't be propagated directly, you need to map it to the return types error type &'static str using map_err(). e.g., fields.next().ok_or("Missing field")?.parse().map_err(|_| "Invalid good deeds")?.

  • Create the Kid Pass the extracted values to Kid::new to build the Kid struct.

  • Return a Result Use Ok for success and meaningful error messages (like "Invalid good deeds") for failures.