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 StderrLogger
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?
use std::fmt::Display; pub trait Logger { /// Log a message at the given verbosity level. fn log(&self, verbosity: u8, message: impl Display); } struct StderrLogger; impl Logger for StderrLogger { fn log(&self, verbosity: u8, message: impl Display) { eprintln!("verbosity={verbosity}: {message}"); } } fn do_things(logger: &impl Logger) { logger.log(5, "FYI"); logger.log(2, "Uhoh"); } // TODO: Define and implement `VerbosityFilter`. fn main() { let l = VerbosityFilter { max_verbosity: 3, inner: StderrLogger }; do_things(&l); }