Moose::Cookbook::Recipe7(3pm)

Usage

  package Point;
  use Moose;
  has 'x' => (isa => 'Int', is => 'ro');
  has 'y' => (isa => 'Int', is => 'rw');
  __PACKAGE__->meta->make_immutable;

Overview

The Moose metaclass API provides a method "make_immutable()". At a high level, this calling this method does two things to your class. One, it makes it faster. In particular, object construction and accessors are effectively "inlined" in your class, and no longer go through the meta-object system.

Second, you can no longer make changes via the metaclass API such as adding attributes. In practice, this won't be a problem, as you don't usually need to do this at runtime after first loading the class.

Immutabilization and "new()"

If you override "new()" in your class, then the immutabilization code will not be able to provide an optimized constructor for your class. Instead, consider providing a "BUILD()" method. You can probably do the same thing in a "BUILD()" method.

Alternately, if you really need to provide a different "new()", you can also provide your own immutabilization method.

Discussing this is beyond the scope of this recipe, however.

Conclusion

We strongly recommend you make your classes immutable. It makes your code much faster, basically for free. This will be especially noticeable when creating many objects or calling accessors frequently.

Copyright and license

<http://www.iinteractive.com>

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.