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Version-4 UUIDs — 122 random bits in the one format every database, log pipeline and API on earth already accepts.

Version

1.0.0 github:retupmoca

Depends

nothing outside the core

License

see the source

Its own test suite

1 file, green

Checked

2026-08-28 against Raku++ 3.20.1 and Rakudo 2026.08

Where it lives

raku.land · source

Install it #

$ rakupp install UUID

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

What it is for #

You need an identifier that is unique without asking anyone — no counter to coordinate, no database round-trip, safe to mint on two machines at once. That is what a version-4 UUID is: 122 random bits dressed in the 8-4-4-4-12 hex format everything already parses. This module makes them and nothing else:

use UUID;

my $id = UUID.new;
say "report-{$id}.json";

report-6decb98e-62d2-4532-abff-e5f3139f4ade.json

Interpolation calls .Str, which renders the canonical dashed form. Note that say $id on its own prints the object's constructor gist — bytes and all — so when you want the familiar string, interpolate or call .Str yourself.

What the format promises #

Two nibbles in a v4 UUID are not random: the third group starts with 4 (the version) and the fourth with one of 8 9 a b (the variant). Those are the bits a validator checks, and this page can check them the same way — everything below is deterministic even though every UUID is fresh:

use UUID;

my $id = UUID.new;
say $id.Str.chars;
say so $id.Str ~~ /^ <xdigit>**8 '-' <xdigit>**4 '-' 4 <xdigit>**3 '-' <[89ab]> <xdigit>**3 '-' <xdigit>**12 $/;
say $id.version;
say $id.Blob.elems;
say UUID.new.Str ne UUID.new.Str;

36
True
4
16
True

.Blob hands you the sixteen raw bytes for the protocols that want binary, and .version reports the 4. The last line is the practical guarantee: two calls, two values — with 122 random bits, a collision is not something to code for.

Only version 4 is implemented; UUID.new(:version(1)) — the timestamp-and-MAC flavour — dies with UUID version 1 not supported, which is the module telling you its whole scope honestly. If you need the newer sortable kinds (v7), this is not the distribution for them.

Where the two engines differ #

Nothing on this page. The random source, the version and variant bit stamping, the string form and the raw bytes behave identically under Raku++ and Rakudo — including the unhelpful default say gist, which both engines print the same way.

What was run to put this page here #

1. Parse — every file of the distribution is parsed by Raku++ itself.
2. Install — rakupp install UUID; it depends on nothing outside the core.
3. Test — the distribution's own suite: 1 file, green.
4. Run — every example on this page under each engine as the site is built — the first example once per engine (its output is fresh every run, so it is shown as one run), the second twice, with every line compared.

Seventeen distributions depend on it, which for a module this small — one class, forty lines — is the ecosystem saying the scope is exactly right.