---
name: "MooseX::SetOnce"
section: "3pm"
platform: "linux"
package: "libmoosex-setonce-perl"
version: "0.200002-2"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/MooseX::SetOnce"
---

# MooseX::SetOnce(3pm)

write-once, read-many attributes for Moose

## NAME

MooseX::SetOnce - write-once, read-many attributes for Moose

## VERSION

version 0.200002

## SYNOPSIS

Add the "SetOnce" trait to attributes:

```
  package Class;
  use Moose;
  use MooseX::SetOnce;
  has some_attr => (
    is     => 'rw',
    traits => [ qw(SetOnce) ],
  );
```

...and then 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!
```

## DESCRIPTION

The 'SetOnce' attribute lets your class have attributes that are not lazy and not set, but that cannot be altered once set.

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.

If the attribute has a clearer, you may clear the attribute and set it again.

## AUTHOR

Ricardo SIGNES \<rjbs@cpan.org\>

## COPYRIGHT AND LICENSE

This software is copyright (c) 2013 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.