“`rust
fn parse(line: &str) -> Result<(String, f64), RowError> {
let f: Vec<&str> = line.split(‘,’).collect();
if f.len() < 5 { return Err(RowError::Missing); }
let qty: f64 = f[3].trim().parse().map_err(|_| RowError::BadNumber(f[3].to_string()))?;
let rate: f64 = f[4].trim().parse().map_err(|_| RowError::BadNumber(f[4].to_string()))?;
Ok((f[1].to_string(), qty * rate))
}
```
Functions that can fail return Result<T, E>: Ok(value) or Err(error). The ? operator returns the error early. Option<T> (Some/None) replaces null.
⚠️ unwrap() crashes on errors. Fine for quick experiments; use match, ? or expect(“clear message”) in real code.
Code for this course follows standard, current syntax; we test JavaScript and PowerShell scripts before publishing, and R/Java/Rust examples are kept to core language features. Tell us if anything fails on your setup.
Practice
Run the project file with a broken line added to sales.csv and watch it skip that row.
