# Class::ISA - phpMan

## NAME
    [Class::ISA] - report the search path for a class's ISA tree

## 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
    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
        element.

    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.

## CAUTIONARY NOTES
    * [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
    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@cpan.org>"

## MAINTAINER
    Maintained by Steffen Mueller "<smueller@cpan.org>".