Attribute::Util - A selection of general-utility attributes


Attribute::Util - A selection of general-utility attributes


  use Attribute::Util;
  # Alias
  sub color : Alias(colour) { return 'red' }
  # Abstract
  package MyObj;
  sub new { ... }
  sub somesub: Abstract;
  package MyObj::Better;
  use base 'MyObj';
  sub somesub { return "I'm implemented!" }
  # Memoize
  sub fib :Memoize {
          my $n = shift;
          return $n if $n < 2;
          fib($n-1) + fib($n-2);

  print fib($_),"\n" for 1..50;
  # SigHandler
  sub myalrm : SigHandler(ALRM, VTALRM) { ...  }
  sub mywarn : SigHandler(__WARN__) { ... }


This module provides four universally accessible attributes of general interest:

This attribute makes it slightly easier (and modern) to memoize a function by providing an attribute, :Memoize that makes it unnecessary for you to explicitly call Memoize::memoize(). Options can be passed via the attribute per usual (see the Attribute::Handlers manpage for details, and the Memoize manpage for information on memoizing options):
  sub f :Memoize(NORMALIZER => 'main::normalize_f') {

However, since the call to memoize() is now done in a different package, it is necessary to include the package name in any function names passed as options to the attribute, as shown above.

Declaring a subroutine to be abstract using this attribute causes a call to it to die with a suitable exception. Subclasses are expected to implement the abstract method.

Using the attribute makes it visually distinctive that a method is abstract, as opposed to declaring it without any attribute or method body, or providing a method body that might make it look as though it was implemented after all.

If you need a variable or subroutine to be known by another name, use this attribute. Internally, the attribute's handler assigns typeglobs to each other. As such, the Alias attribute provides a layer of abstraction. If the underlying mechanism changes in a future version of Perl (say, one that might not have the concept of typeglobs anymore :), a new version of this module will take care of that, but your Alias declarations are going to stay the same.

Note that assigning typeglobs means that you can't specify a synonym for one element of the glob and use the same synonym for a different target name in a different slot. I.e.,

  sub color :Alias(colour) { ... }
  my $farbe :Alias(colour);

doesn't make sense, since the sub declaration aliases the whole colour glob to color, but then the scalar declaration aliases the whole colour glob to farbe, so the first alias is lost.

When used on a subroutine, this attribute declares that subroutine to be a signal handler for the signal(s) given as options for this attribute. It thereby frees you from the implementation details of defining sig handlers and keeps the handler definitions where they belong, namely with the handler subroutine.


None known so far. If you find any bugs or oddities, please do inform the author.


Marcel Grunauer, <>


Copyright 2001 Marcel Grunauer. All rights reserved.

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


perl(1), Attribute::Handlers(3pm), Memoize(3pm).

 Attribute::Util - A selection of general-utility attributes