Distribution · debugging

Logger

Works

The continuation of the Log distribution under a new name — the same levels, pattern and contexts, plus a settable pattern and a hook for the timestamp.

Version: 0.4.6 zef:whity
Depends: nothing outside the core
License: Artistic-2.0
Its own test suite: 6 files, green
Checked: 2026-09-15 against Raku++ 3.28.0 and Rakudo 2026.08
Where it lives: raku.land · source

Install it #

$ rakupp install Logger

zef install Logger writes the same store; either installer leaves the module usable by both engines.

What it is for #

This is the same codebase as Log, from the same repository, under the name its author settled on. Everything on the Log page applies: five levels, a pattern string, a registry of named loggers, and the nested and mapped context stores.

Two things are different, and they are the two that matter most in practice. The pattern can be changed after construction, and the timestamp has a hook — which is what makes a logger testable, because a line with a live clock in it cannot be compared against anything.

A pinned timestamp #

File

use Logger;

my $log = Logger.new(
    level        => Logger::INFO,
    dt-formatter => sub ($dt) { 'TS' },
);
$log.error('disk on fire');
$log.warn('disk warm');
$log.info('disk fine');
$log.debug('dropped: level is INFO');

$log.level = Logger::TRACE;
$log.debug('now it appears');

$log.pattern = '[%c] %m%n';
$log.info('a different layout');

Output

[TS][ERROR] disk on fire
[TS][WARN] disk warm
[TS][INFO] disk fine
[TS][DEBUG] now it appears
[INFO] a different layout

dt-formatter replaces the %d placeholder's value, and a formatter that ignores its argument and returns a constant is what a test wants. The default pattern includes %d, so without this every line carries the current time and nothing about the output is reproducible.

The formatter is handed the DateTime, so a real one can format it however the deployment wants:

File

use Logger;

my $log = Logger.new(level => Logger::INFO, pattern => '[%d] %m%n');

$log.dt-formatter = sub ($x) { 'given a ' ~ $x.^name };
$log.info('what does the hook receive?');

$log.dt-formatter = sub ($dt) {
    sprintf('%04d-%02d-%02d', $dt.year, $dt.month, $dt.day)
};
$log.info('a date only');

my $a = Logger.new(level => Logger::INFO, pattern => '[%x] %m%n');
$a.ndc.push('orig');
my $b = $a.clone;
$b.ndc.push('cloned-only');
$a.info('from the original');
$b.info('from the clone');

Output

[given a DateTime] what does the hook receive?
[2026-09-15] a date only
[orig] from the original
[orig cloned-only] from the clone

clone copies the contexts by value, so the two loggers diverge from the moment they are cloned — which is what you want when a request handler takes a copy of the application logger and adds its own request identifier.

The one thing to know #

The shipped default formatter names its parameter $self, and it is not the logger — it is the DateTime:

# the default, as shipped
sub ($self) { DateTime.now.Str }

It ignores its argument and reads the clock a second time. So anyone who writes a formatter trusting that name will reach for logger methods on a DateTime and get a method-not-found error that makes no sense. The first example above probes it and prints what actually arrives.

Everything on the Log page's warning about pattern-escape injection applies here unchanged: the message goes into the pattern before the other placeholders are expanded, so a logged string containing %p or %X{…} has them interpolated. Under the Raku++ 3.28.0 release the class-level registry was dead here — Logger.get returned nothing, because the engine did not resolve the compile-time class name the registry keys on. That is fixed, and both spellings work now.

If you are choosing between the two distributions: use this one. They are the same code, and Log is the older name. Do not load both — you get two registries and two incompatible level enumerations.