slog 0.3.0

Structured, composable logging for Rust


Code snippet

fn main() {
    // Create a new group of loggers, sharing one drain.
    let root = root_logger!("version" => VERSION);

    // Child loggers clone the `key: values` pairs from their parents.
    let _log = child_logger!(root, "child" => 1);

    // Closures can be used for values that change at runtime.
    // Data captured by the closure needs to be `Send+Sync`.
    let counter = Arc::new(AtomicUsize::new(0));
    let log = child_logger!(root, "counter" => {
        let counter = counter.clone();
        move || { counter.load(SeqCst)}

    info!(log, "before-fetch-add"); // counter == 0
    counter.fetch_add(1, SeqCst);
    info!(log, "after-fetch-add"); // counter == 1

    // Drains can be swapped atomically (race-free).
        // drains are composable
                // multiple outputs formats are supported

    // Closures can be used for lazy evaluation:
    // This `slow_fib` won't be evaluated, as the current drain discards
    // "trace" level logging records.
    trace!(log, "trace", "lazy-closure" => Box::new(move || slow_fib(40)));

    // Loggers are internally atomically reference counted so can be cloned,
    // passed between threads and stored without hassle.
    let join = thread::spawn({
        let log = log.clone();
        move || {
            info!(log, "subthread", "stage" => "start");
            thread::sleep(Duration::new(1, 0));
            info!(log, "subthread", "stage" => "end");


See examples/ for full code.


Structured, composable logging for Rust. Work in progress, but usable already.

Heavily inspired by log15 for Go, which I liked so much, that I want it in Rust too.

Read Documentation for details and features.

If you want to say hi, or need help use #dpc

To report a bug or ask for features use github issues.

Building & running

If you need to install Rust (come on, you should have done that long time ago!), use rustup.

In your project

In Cargo.toml:

slog = "*"

In your

extern crate slog;