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129 | .\" ======================================================================== | |
130 | .\" | |
131 | .IX Title "Class::ISA 3" | |
132 | .TH Class::ISA 3 "2001-09-21" "perl v5.8.8" "Perl Programmers Reference Guide" | |
133 | .SH "NAME" | |
134 | Class::ISA \-\- report the search path for a class's ISA tree | |
135 | .SH "SYNOPSIS" | |
136 | .IX Header "SYNOPSIS" | |
137 | .Vb 4 | |
138 | \& # Suppose you go: use Food::Fishstick, and that uses and | |
139 | \& # inherits from other things, which in turn use and inherit | |
140 | \& # from other things. And suppose, for sake of brevity of | |
141 | \& # example, that their ISA tree is the same as: | |
142 | .Ve | |
143 | .PP | |
144 | .Vb 7 | |
145 | \& @Food::Fishstick::ISA = qw(Food::Fish Life::Fungus Chemicals); | |
146 | \& @Food::Fish::ISA = qw(Food); | |
147 | \& @Food::ISA = qw(Matter); | |
148 | \& @Life::Fungus::ISA = qw(Life); | |
149 | \& @Chemicals::ISA = qw(Matter); | |
150 | \& @Life::ISA = qw(Matter); | |
151 | \& @Matter::ISA = qw(); | |
152 | .Ve | |
153 | .PP | |
154 | .Vb 4 | |
155 | \& use Class::ISA; | |
156 | \& print "Food::Fishstick path is:\en ", | |
157 | \& join(", ", Class::ISA::super_path('Food::Fishstick')), | |
158 | \& "\en"; | |
159 | .Ve | |
160 | .PP | |
161 | That prints: | |
162 | .PP | |
163 | .Vb 2 | |
164 | \& Food::Fishstick path is: | |
165 | \& Food::Fish, Food, Matter, Life::Fungus, Life, Chemicals | |
166 | .Ve | |
167 | .SH "DESCRIPTION" | |
168 | .IX Header "DESCRIPTION" | |
169 | Suppose you have a class (like Food::Fish::Fishstick) that is derived, | |
170 | via its \f(CW@ISA\fR, from one or more superclasses (as Food::Fish::Fishstick | |
171 | is from Food::Fish, Life::Fungus, and Chemicals), and some of those | |
172 | superclasses may themselves each be derived, via its \f(CW@ISA\fR, from one or | |
173 | more superclasses (as above). | |
174 | .PP | |
175 | When, then, you call a method in that class ($fishstick\->calories), | |
176 | Perl first searches there for that method, but if it's not there, it | |
177 | goes searching in its superclasses, and so on, in a depth-first (or | |
178 | maybe \*(L"height\-first\*(R" is the word) search. In the above example, it'd | |
179 | first look in Food::Fish, then Food, then Matter, then Life::Fungus, | |
180 | then Life, then Chemicals. | |
181 | .PP | |
182 | This library, Class::ISA, provides functions that return that list \*(-- | |
183 | the list (in order) of names of classes Perl would search to find a | |
184 | method, with no duplicates. | |
185 | .SH "FUNCTIONS" | |
186 | .IX Header "FUNCTIONS" | |
187 | .IP "the function Class::ISA::super_path($CLASS)" 4 | |
188 | .IX Item "the function Class::ISA::super_path($CLASS)" | |
189 | This returns the ordered list of names of classes that Perl would | |
190 | search thru in order to find a method, with no duplicates in the list. | |
191 | \&\f(CW$CLASS\fR is not included in the list. \s-1UNIVERSAL\s0 is not included \*(-- if | |
192 | you need to consider it, add it to the end. | |
193 | .IP "the function Class::ISA::self_and_super_path($CLASS)" 4 | |
194 | .IX Item "the function Class::ISA::self_and_super_path($CLASS)" | |
195 | Just like \f(CW\*(C`super_path\*(C'\fR, except that \f(CW$CLASS\fR is included as the first | |
196 | element. | |
197 | .IP "the function Class::ISA::self_and_super_versions($CLASS)" 4 | |
198 | .IX Item "the function Class::ISA::self_and_super_versions($CLASS)" | |
199 | This returns a hash whose keys are \f(CW$CLASS\fR and its | |
200 | (super\-)superclasses, and whose values are the contents of each | |
201 | class's \f(CW$VERSION\fR (or undef, for classes with no \f(CW$VERSION\fR). | |
202 | .Sp | |
203 | The code for self_and_super_versions is meant to serve as an example | |
204 | for precisely the kind of tasks I anticipate that self_and_super_path | |
205 | and super_path will be used for. You are strongly advised to read the | |
206 | source for self_and_super_versions, and the comments there. | |
207 | .SH "CAUTIONARY NOTES" | |
208 | .IX Header "CAUTIONARY NOTES" | |
209 | * Class::ISA doesn't export anything. You have to address the | |
210 | functions with a \*(L"Class::ISA::\*(R" on the front. | |
211 | .PP | |
212 | * Contrary to its name, Class::ISA isn't a class; it's just a package. | |
213 | Strange, isn't it? | |
214 | .PP | |
215 | * Say you have a loop in the \s-1ISA\s0 tree of the class you're calling one | |
216 | of the Class::ISA functions on: say that Food inherits from Matter, | |
217 | but Matter inherits from Food (for sake of argument). If Perl, while | |
218 | searching for a method, actually discovers this cyclicity, it will | |
219 | throw a fatal error. The functions in Class::ISA effectively ignore | |
220 | this cyclicity; the Class::ISA algorithm is \*(L"never go down the same | |
221 | path twice\*(R", and cyclicities are just a special case of that. | |
222 | .PP | |
223 | * The Class::ISA functions just look at \f(CW@ISAs\fR. But theoretically, I | |
224 | suppose, AUTOLOADs could bypass Perl's ISA-based search mechanism and | |
225 | do whatever they please. That would be bad behavior, tho; and I try | |
226 | not to think about that. | |
227 | .PP | |
228 | * If Perl can't find a method anywhere in the \s-1ISA\s0 tree, it then looks | |
229 | in the magical class \s-1UNIVERSAL\s0. This is rarely relevant to the tasks | |
230 | that I expect Class::ISA functions to be put to, but if it matters to | |
231 | you, then instead of this: | |
232 | .PP | |
233 | .Vb 1 | |
234 | \& @supers = Class::Tree::super_path($class); | |
235 | .Ve | |
236 | .PP | |
237 | do this: | |
238 | .PP | |
239 | .Vb 1 | |
240 | \& @supers = (Class::Tree::super_path($class), 'UNIVERSAL'); | |
241 | .Ve | |
242 | .PP | |
243 | And don't say no-one ever told ya! | |
244 | .PP | |
245 | * When you call them, the Class::ISA functions look at \f(CW@ISAs\fR anew \*(-- | |
246 | that is, there is no memoization, and so if ISAs change during | |
247 | runtime, you get the current \s-1ISA\s0 tree's path, not anything memoized. | |
248 | However, changing ISAs at runtime is probably a sign that you're out | |
249 | of your mind! | |
250 | .SH "COPYRIGHT" | |
251 | .IX Header "COPYRIGHT" | |
252 | Copyright (c) 1999, 2000 Sean M. Burke. All rights reserved. | |
253 | .PP | |
254 | This library is free software; you can redistribute it and/or modify | |
255 | it under the same terms as Perl itself. | |
256 | .SH "AUTHOR" | |
257 | .IX Header "AUTHOR" | |
258 | Sean M. Burke \f(CW\*(C`sburke@cpan.org\*(C'\fR |