info > Class::ISA

Class::ISA(3pm)

📖 NAME

Class::ISA - report the search path for a class's ISA tree

🚀 Quick Reference

Use Case	Command	Description
Get inheritance path (excluding self)	use Class::ISA; my @path = Class::ISA::super_path('Food::Fishstick');	Returns ordered list of superclasses Perl would search for a method, with no duplicates.
Get inheritance path including self	my @path = Class::ISA::self_and_super_path('Food::Fishstick');	Same as super_path but includes the class itself as first element.
Get class versions along inheritance tree	my %versions = Class::ISA::self_and_super_versions('Food::Fishstick');	Returns hash keyed by class name (including self) with values from each class's $VERSION (or undef).

📋 SYNOPSIS

  # Suppose you go: use Food::Fishstick, and that uses and
  # inherits from other things, which in turn use and inherit
  # from other things.  And suppose, for sake of brevity of
  # example, that their ISA tree is the same as:

  @Food::Fishstick::ISA = qw(Food::Fish  Life::Fungus  Chemicals);
  @Food::Fish::ISA = qw(Food);
  @Food::ISA = qw(Matter);
  @Life::Fungus::ISA = qw(Life);
  @Chemicals::ISA = qw(Matter);
  @Life::ISA = qw(Matter);
  @Matter::ISA = qw();

  use Class::ISA;
  print "Food::Fishstick path is:\n ",
        join(", ", Class::ISA::super_path('Food::Fishstick')),
        "\n";

That prints:

  Food::Fishstick path is:
   Food::Fish, Food, Matter, Life::Fungus, Life, Chemicals

📝 DESCRIPTION

Suppose you have a class (like Food::Fish::Fishstick) that is derived, via its @ISA, from one or more superclasses (as Food::Fish::Fishstick is from Food::Fish, Life::Fungus, and Chemicals), and some of those superclasses may themselves each be derived, via its @ISA, from one or more superclasses (as above).

When, then, you call a method in that class ($fishstick->calories), Perl first searches there for that method, but if it's not there, it goes searching in its superclasses, and so on, in a depth-first (or maybe "height-first" is the word) search. In the above example, it'd first look in Food::Fish, then Food, then Matter, then Life::Fungus, then Life, then Chemicals.

This library, Class::ISA, provides functions that return that list — the list (in order) of names of classes Perl would search to find a method, with no duplicates.

⚙️ FUNCTIONS

• Class::ISA::super_path($CLASS) — Returns the ordered list of names of classes that Perl would search thru in order to find a method, with no duplicates. $CLASS is not included. UNIVERSAL is not included — if you need to consider it, add it to the end.
• Class::ISA::self_and_super_path($CLASS) — Just like super_path, except that $CLASS is included as the first element.
• Class::ISA::self_and_super_versions($CLASS) — Returns a hash whose keys are $CLASS and its superclasses, and whose values are the contents of each class's $VERSION (or undef for classes with no $VERSION). The code is meant to serve as an example for the kind of tasks anticipated for self_and_super_path and super_path. You are strongly advised to read the source for self_and_super_versions and the comments there.

⚠️ CAUTIONARY NOTES

• 🔹 Class::ISA doesn't export anything. You must address the functions with a Class::ISA:: prefix.
• 🔹 Contrary to its name, Class::ISA isn't a class; it's just a package. Strange, isn't it?
• 🔹 Say you have a loop in the ISA tree — e.g., Food inherits from Matter, but Matter inherits from Food. If Perl discovers this cyclicity while searching for a method, it throws a fatal error. The functions in Class::ISA effectively ignore this cyclicity; the algorithm is "never go down the same path twice", and cyclicities are just a special case of that.
• 🔹 The Class::ISA functions just look at @ISAs. But theoretically, AUTOLOADs could bypass Perl's ISA-based search mechanism and do whatever they please. That would be bad behavior, though.
• 🔹 If Perl can't find a method anywhere in the ISA tree, it then looks in the magical class UNIVERSAL. This is rarely relevant to the tasks expected of Class::ISA functions, but if it matters to you, instead of @supers = Class::Tree::super_path($class);, do @supers = (Class::Tree::super_path($class), 'UNIVERSAL');.
• 🔹 When you call them, the Class::ISA functions look at @ISAs anew — there is no memoization, so if @ISAs change during runtime, you get the current ISA tree's path, not anything memoized. However, changing @ISAs at runtime is probably a sign that you're out of your mind!

©️ COPYRIGHT AND LICENSE

Copyright (c) 1999-2009 Sean M. Burke. All rights reserved.

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

👤 AUTHOR

Sean M. Burke <sburke AT cpan.org>

🛠️ MAINTAINER

Maintained by Steffen Mueller <smueller AT cpan.org>