`Try Operator

Runtime errors like connection-refused or file-not-found are handled with the Result type, but matching this type on every call can be cumbersome. The try-operator ? is used to return errors to the caller. It lets you turn the common

match some_expression {
    Ok(value) => value,
    Err(err) => return Err(err),
}

into the much simpler

some_expression?

We can use this to simplify our error handling code:

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Speaker Notes

 This slide should take about 5 minutes.

Simplify the read_username function to use ?.

Schlüsselpunkte:

  • The username variable can be either Ok(string) or Err(error).
  • Use the fs::write call to test out the different scenarios: no file, empty file, file with username.
  • Note that main can return a Result<(), E> as long as it implements std::process::Termination. In practice, this means that E implements Debug. The executable will print the Err variant and return a nonzero exit status on error.