Macro slog::log

macro_rules! log {
    ($l:expr, $lvl:expr,  $tag:expr, $($k:expr => $v:expr),+; $($args:tt)+ ) => { ... };
    ($l:expr, $lvl:expr, $tag:expr, $msg:expr,) => { ... };
    ($l:expr, $lvl:expr, $tag:expr, $msg:expr) => { ... };
    ($l:expr, $lvl:expr, $tag:expr, $msg:expr; $($k:expr => $v:expr),+,) => { ... };
    ($l:expr, $lvl:expr, $tag:expr, $msg:expr; $($k:expr => $v:expr),+) => { ... };
    ($l:expr, $lvl:expr, $tag:expr, $($args:tt)+) => { ... };
}

Log message a logging record

Use wrappers error!, warn! etc. instead

The max_level_* and release_max_level* cargo features can be used to statically disable logging at various levels. See slog notable details

Use version with longer name if you want to prevent clash with legacy log crate macro names.

Supported invocations

Simple

#[macro_use]
extern crate slog;

fn main() {
    let drain = slog::Discard;
    let root = slog::Logger::root(
        drain,
        o!("key1" => "value1", "key2" => "value2")
    );
    info!(root, "test info log"; "log-key" => true);
}

Note that "key" => value part is optional:

#[macro_use]
extern crate slog;

fn main() {
    let drain = slog::Discard;
    let root = slog::Logger::root(
        drain, o!("key1" => "value1", "key2" => "value2")
    );
    info!(root, "test info log");
}

fmt::Arguments support:

#[macro_use]
extern crate slog;

fn main() {
    let drain = slog::Discard;
    let root = slog::Logger::root(drain,
        o!("key1" => "value1", "key2" => "value2")
    );
    info!(root, "log-key" => true; "formatted: {}", 1);
}

Note that due to macro parsing limitation, the message was moved after the key-value pairs.

Again, "key" => value part is optional:

#[macro_use]
extern crate slog;

fn main() {
    let drain = slog::Discard;
    let root = slog::Logger::root(
        drain, o!("key1" => "value1", "key2" => "value2")
    );
    info!(root, "formatted: {}", 1);
}

Note: use formatting support only when it really makes sense. Eg. logging message like "found {} keys" is against structured logging. It should be "found keys", "count" => keys_num instead, so that data is clearly named, typed and separated from the message.

Tags

All above versions can be supplemented with a tag - string literal prefixed with #.

#[macro_use]
extern crate slog;

fn main() {
    let drain = slog::Discard;
    let root = slog::Logger::root(drain,
        o!("key1" => "value1", "key2" => "value2")
    );
    let ops = 3;
    info!(
        root,
        #"performance-metric", "thread speed"; "ops_per_sec" => ops
    );
}

See Record::tag() for more information about tags.