Class::ISA man page on aLinux

Man page or keyword search:  
man Server   7435 pages
apropos Keyword Search (all sections)
Output format
aLinux logo
[printable version]

Class::ISA(3)	       Perl Programmers Reference Guide		 Class::ISA(3)

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

	 # 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')),

       That prints:

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

       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.

       the function Class::ISA::super_path($CLASS)
	   This returns the ordered list of names of classes that Perl would
	   search thru in order to find a method, with no duplicates in the
	   list.  $CLASS is not included in the list.  UNIVERSAL is not
	   included -- if you need to consider it, add it to the end.

       the function Class::ISA::self_and_super_path($CLASS)
	   Just like "super_path", except that $CLASS is included as the first

       the function Class::ISA::self_and_super_versions($CLASS)
	   This returns a hash whose keys are $CLASS and its
	   (super-)superclasses, and whose values are the contents of each
	   class's $VERSION (or undef, for classes with no $VERSION).

	   The code for self_and_super_versions is meant to serve as an
	   example for precisely the kind of tasks I anticipate that
	   self_and_super_path and super_path will be used for.	 You are
	   strongly advised to read the source for self_and_super_versions,
	   and the comments there.

       * Class::ISA doesn't export anything.  You have to address the
       functions with a "Class::ISA::" on the front.

       * 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 of the class you're calling one
       of the Class::ISA functions on: say that Food inherits from Matter, but
       Matter inherits from Food (for sake of argument).  If Perl, while
       searching for a method, actually discovers this cyclicity, it will
       throw a fatal error.  The functions in Class::ISA effectively ignore
       this cyclicity; the Class::ISA 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, I
       suppose, AUTOLOADs could bypass Perl's ISA-based search mechanism and
       do whatever they please.	 That would be bad behavior, tho; and I try
       not to think about that.

       * 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
       that I expect Class::ISA functions to be put to, but if it matters to
       you, then instead of this:

	 @supers = Class::Tree::super_path($class);

       do this:

	 @supers = (Class::Tree::super_path($class), 'UNIVERSAL');

       And don't say no-one ever told ya!

       * When you call them, the Class::ISA functions look at @ISAs anew --
       that is, there is no memoization, and 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

       Copyright (c) 1999, 2000 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.

       Sean M. Burke ""

perl v5.10.0			  2007-12-18			 Class::ISA(3)

List of man pages available for aLinux

Copyright (c) for man pages and the logo by the respective OS vendor.

For those who want to learn more, the polarhome community provides shell access and support.

[legal] [privacy] [GNU] [policy] [cookies] [netiquette] [sponsors] [FAQ]
Polarhome, production since 1999.
Member of Polarhome portal.
Based on Fawad Halim's script.
Vote for polarhome
Free Shell Accounts :: the biggest list on the net