Exercise: Logger Trait

Let’s design a simple logging utility, using a trait Logger with a log method. Code which might log its progress can then take an &impl Logger. In testing, this might put messages in the test logfile, while in a production build it would send messages to a log server.

However, the StdoutLogger given below logs all messages, regardless of verbosity. Your task is to write a VerbosityFilter type that will ignore messages above a maximum verbosity.

This is a common pattern: a struct wrapping a trait implementation and implementing that same trait, adding behavior in the process. What other kinds of wrappers might be useful in a logging utility?

  1. pub trait Logger {
  2.     /// Log a message at the given verbosity level.
  3.     fn log(&self, verbosity: u8, message: &str);
  4. }
  6. struct StdoutLogger;
  8. impl Logger for StdoutLogger {
  9.     fn log(&self, verbosity: u8, message: &str) {
  10.         println!("verbosity={verbosity}: {message}");
  11.     }
  12. }
  14. // TODO: Define and implement `VerbosityFilter`.
  16. fn main() {
  17.     let logger = VerbosityFilter { max_verbosity: 3, inner: StdoutLogger };
  18.     logger.log(5, "FYI");
  19.     logger.log(2, "Uhoh");
  20. }