MooseX::SetOnce(3)

✨ MooseX::SetOnce ✨

okay bestie, welcome to MooseX::SetOnce — it's a User Contributed Perl Documentation page and it's literally about making attributes that you can write once and read many times 💅 no cap.

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🎀 NAME 🎀

MooseX::SetOnce — write-once, read-many attributes for Moose. it's giving "one and done" energy fr fr 🦋

🌸 VERSION 🌸

version 0.203 ✨ (yes queen, that's the number, don't come for me)

👑 SYNOPSIS 👑

so first you gotta add the "SetOnce" trait to your attributes, like this:

package Class;
use Moose;
use MooseX::SetOnce;

has some_attr => (
  is     => 'rw',
  traits => [ qw(SetOnce) ],
);

...and then bestie, you can only set them once:

my $object = Class->new;

$object->some_attr(10);  # works fine
$object->some_attr(20);  # throws an exception: it's already set!

like. the second one is a whole exception. it said no. periodt. 😭

💖 DESCRIPTION 💖

The 'SetOnce' attribute lets your class have attributes that are not lazy and not set, but that cannot be altered once set. it's the "you had your chance, the door is closed now" of attributes 🚪✨

The logic is very simple: if you try to alter the value of an attribute with the SetOnce trait — either by accessor or writer — and the attribute has a value, it will throw an exception. that's it, that's the whole vibe. 💀

and ngl, if the attribute has a clearer, you may clear the attribute and set it again. so there's a lil escape hatch, bestie 🫶

🌈 PERL VERSION 🌈

This library should run on perls released even a long time ago. It should work on any version of perl released in the last five years. iconic, honestly. 👑

Although it may work on older versions of perl, no guarantee is made that the minimum required version will not be increased. The version may be increased for any reason, and there is no promise that patches will be accepted to lower the minimum required perl. so like, don't be surprised, iykyk 🙈

💜 AUTHOR 💜

Ricardo SIGNES <cpan@semiotic.systems> — the main character, fr fr 👑

🧚 CONTRIBUTORS 🧚

• Jesse Luehrs <doy@tozt.net>
• Karen Etheridge <ether@cpan.org>
• Kent Fredric <kentfredric@gmail.com>
• Ricardo Signes <rjbs@semiotic.systems>

all legends, all ate, no crumbs left 💅✨

⭐ COPYRIGHT AND LICENSE ⭐

This software is copyright (c) 2022 by Ricardo SIGNES.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself. slay, open source, we love to see it 🫶🌈

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perl v5.42.0 · 2025-07-25 — and that's the whole MooseX::SetOnce(3) page bestie, mwah, go set your attributes exactly one time 💋🎀🦋