#!/usr/local/bin/perl # Time-stamp: "2004-12-29 20:01:02 AST" -*-Perl-*- package Class::ISA; require 5; use strict; use vars qw($Debug $VERSION); $VERSION = '0.33'; $Debug = 0 unless defined $Debug; =head1 NAME Class::ISA -- report the search path for a class's ISA tree =head1 SYNOPSIS # Suppose you go: use Food::Fishstick, and that uses and # inherits from other things, which in turn use and inherit # from other things. And suppose, for sake of brevity of # example, that their ISA tree is the same as: @Food::Fishstick::ISA = qw(Food::Fish Life::Fungus Chemicals); @Food::Fish::ISA = qw(Food); @Food::ISA = qw(Matter); @Life::Fungus::ISA = qw(Life); @Chemicals::ISA = qw(Matter); @Life::ISA = qw(Matter); @Matter::ISA = qw(); use Class::ISA; print "Food::Fishstick path is:\n ", join(", ", Class::ISA::super_path('Food::Fishstick')), "\n"; That prints: Food::Fishstick path is: Food::Fish, Food, Matter, Life::Fungus, Life, Chemicals =head1 DESCRIPTION Suppose you have a class (like Food::Fish::Fishstick) that is derived, via its @ISA, from one or more superclasses (as Food::Fish::Fishstick is from Food::Fish, Life::Fungus, and Chemicals), and some of those superclasses may themselves each be derived, via its @ISA, from one or more superclasses (as above). When, then, you call a method in that class ($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. =head1 FUNCTIONS =over =item 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. $CLASS is not included in the list. UNIVERSAL is not included -- if you need to consider it, add it to the end. =item the function Class::ISA::self_and_super_path($CLASS) Just like C, except that $CLASS is included as the first element. =item the function Class::ISA::self_and_super_versions($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 $VERSION). The code for self_and_super_versions is meant to serve as an example for precisely the kind of tasks I anticipate that self_and_super_path and super_path will be used for. You are strongly advised to read the source for self_and_super_versions, and the comments there. =back =head1 CAUTIONARY NOTES * Class::ISA doesn't export anything. You have to address the functions with a "Class::ISA::" on the front. * Contrary to its name, Class::ISA isn't a class; it's just a package. Strange, isn't it? * Say you have a loop in the ISA tree of the class you're calling one of the Class::ISA functions on: say that Food inherits from Matter, but Matter inherits from Food (for sake of argument). If Perl, while searching for a method, actually discovers this cyclicity, it will throw a fatal error. The functions in Class::ISA effectively ignore this cyclicity; the Class::ISA algorithm is "never go down the same path twice", and cyclicities are just a special case of that. * The Class::ISA functions just look at @ISAs. But theoretically, I suppose, AUTOLOADs could bypass Perl's ISA-based search mechanism and do whatever they please. That would be bad behavior, tho; and I try not to think about that. * If Perl can't find a method anywhere in the ISA tree, it then looks in the magical class UNIVERSAL. This is rarely relevant to the tasks that I expect Class::ISA functions to be put to, but if it matters to you, then instead of this: @supers = Class::Tree::super_path($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! =head1 COPYRIGHT 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. =head1 AUTHOR Sean M. Burke C =cut ########################################################################### sub self_and_super_versions { no strict 'refs'; map { $_ => (defined(${"$_\::VERSION"}) ? ${"$_\::VERSION"} : undef) } self_and_super_path($_[0]) } # Also consider magic like: # no strict 'refs'; # my %class2SomeHashr = # map { defined(%{"$_\::SomeHash"}) ? ($_ => \%{"$_\::SomeHash"}) : () } # Class::ISA::self_and_super_path($class); # to get a hash of refs to all the defined (and non-empty) hashes in # $class and its superclasses. # # Or even consider this incantation for doing something like hash-data # inheritance: # no strict 'refs'; # %union_hash = # map { defined(%{"$_\::SomeHash"}) ? %{"$_\::SomeHash"}) : () } # reverse(Class::ISA::self_and_super_path($class)); # Consider that reverse() is necessary because with # %foo = ('a', 'wun', 'b', 'tiw', 'a', 'foist'); # $foo{'a'} is 'foist', not 'wun'. ########################################################################### sub super_path { my @ret = &self_and_super_path(@_); shift @ret if @ret; return @ret; } #-------------------------------------------------------------------------- sub self_and_super_path { # Assumption: searching is depth-first. # Assumption: '' (empty string) can't be a class package name. # Note: 'UNIVERSAL' is not given any special treatment. return () unless @_; my @out = (); my @in_stack = ($_[0]); my %seen = ($_[0] => 1); my $current; while(@in_stack) { next unless defined($current = shift @in_stack) && length($current); print "At $current\n" if $Debug; push @out, $current; no strict 'refs'; unshift @in_stack, map { my $c = $_; # copy, to avoid being destructive substr($c,0,2) = "main::" if substr($c,0,2) eq '::'; # Canonize the :: -> main::, ::foo -> main::foo thing. # Should I ever canonize the Foo'Bar = Foo::Bar thing? $seen{$c}++ ? () : $c; } @{"$current\::ISA"} ; # I.e., if this class has any parents (at least, ones I've never seen # before), push them, in order, onto the stack of classes I need to # explore. } return @out; } #-------------------------------------------------------------------------- 1; __END__