log

A Rust library providing a lightweight logging facade.

• log documentation
• env_logger documentation

A logging facade provides a single logging API that abstracts over the actual logging implementation. Libraries can use the logging API provided by this crate, and the consumer of those libraries can choose the logging implementation that is most suitable for its use case.

Usage

In libraries

Libraries should link only to the log crate, and use the provided macros to log whatever information will be useful to downstream consumers:

[dependencies]
log = "0.3"

#[macro_use]
extern crate log;

pub fn shave_the_yak(yak: &Yak) {
    trace!("Commencing yak shaving");

    loop {
        match find_a_razor() {
            Ok(razor) => {
                info!("Razor located: {}", razor);
                yak.shave(razor);
                break;
            }
            Err(err) => {
                warn!("Unable to locate a razor: {}, retrying", err);
            }
        }
    }
}

In executables

Executables should chose a logger implementation and initialize it early in the runtime of the program. Logger implementations will typically include a function to do this. Any log messages generated before the logger is initialized will be ignored.

The executable itself may use the log crate to log as well.

The env_logger crate provides a logger implementation that mirrors the functionality of the old revision of the log crate.

[dependencies]
log = "0.3"
env_logger = "0.3"

#[macro_use]
extern crate log;
extern crate env_logger;

fn main() {
    env_logger::init().unwrap();

    info!("starting up");

    // ...
}