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129 | .\" ======================================================================== |
130 | .\" |
131 | .IX Title "Moose::Cookbook::Meta::Recipe7 3" |
132 | .TH Moose::Cookbook::Meta::Recipe7 3 "2009-03-27" "perl v5.8.7" "User Contributed Perl Documentation" |
133 | .SH "NAME" |
134 | Moose::Cookbook::Meta::Recipe7 \- Creating a glob reference meta\-instance class |
135 | .SH "SYNOPSIS" |
136 | .IX Header "SYNOPSIS" |
137 | .Vb 1 |
138 | \& package My::Meta::Instance; |
139 | .Ve |
140 | .PP |
141 | .Vb 2 |
142 | \& use Scalar::Util qw( weaken ); |
143 | \& use Symbol qw( gensym ); |
144 | .Ve |
145 | .PP |
146 | .Vb 2 |
147 | \& use Moose; |
148 | \& extends 'Moose::Meta::Instance'; |
149 | .Ve |
150 | .PP |
151 | .Vb 5 |
152 | \& sub create_instance { |
153 | \& my $self = shift; |
154 | \& my $sym = gensym(); |
155 | \& bless $sym, $self\->_class_name; |
156 | \& } |
157 | .Ve |
158 | .PP |
159 | .Vb 2 |
160 | \& sub clone_instance { |
161 | \& my ( $self, $instance ) = @_; |
162 | .Ve |
163 | .PP |
164 | .Vb 2 |
165 | \& my $new_sym = gensym(); |
166 | \& %{*$new_sym} = %{*$instance}; |
167 | .Ve |
168 | .PP |
169 | .Vb 2 |
170 | \& bless $new_sym, $self\->_class_name; |
171 | \& } |
172 | .Ve |
173 | .PP |
174 | .Vb 4 |
175 | \& sub get_slot_value { |
176 | \& my ( $self, $instance, $slot_name ) = @_; |
177 | \& return *$instance\->{$slot_name}; |
178 | \& } |
179 | .Ve |
180 | .PP |
181 | .Vb 4 |
182 | \& sub set_slot_value { |
183 | \& my ( $self, $instance, $slot_name, $value ) = @_; |
184 | \& *$instance\->{$slot_name} = $value; |
185 | \& } |
186 | .Ve |
187 | .PP |
188 | .Vb 4 |
189 | \& sub deinitialize_slot { |
190 | \& my ( $self, $instance, $slot_name ) = @_; |
191 | \& delete *$instance\->{$slot_name};; |
192 | \& } |
193 | .Ve |
194 | .PP |
195 | .Vb 4 |
196 | \& sub is_slot_initialized { |
197 | \& my ( $self, $instance, $slot_name, $value ) = @_; |
198 | \& exists *$instance\->{$slot_name};; |
199 | \& } |
200 | .Ve |
201 | .PP |
202 | .Vb 4 |
203 | \& sub weaken_slot_value { |
204 | \& my ( $self, $instance, $slot_name ) = @_; |
205 | \& weaken *$instance\->{$slot_name};; |
206 | \& } |
207 | .Ve |
208 | .PP |
209 | .Vb 4 |
210 | \& sub inline_create_instance { |
211 | \& my ( $self, $class_variable ) = @_; |
212 | \& return 'do { my $sym = Symbol::gensym(); bless $sym, ' . $class_variable . ' }'; |
213 | \& } |
214 | .Ve |
215 | .PP |
216 | .Vb 4 |
217 | \& sub inline_slot_access { |
218 | \& my ( $self, $instance, $slot_name ) = @_; |
219 | \& return '*{' . $instance . '}\->{' . $slot_name . '}'; |
220 | \& } |
221 | .Ve |
222 | .PP |
223 | .Vb 1 |
224 | \& package MyApp::User; |
225 | .Ve |
226 | .PP |
227 | .Vb 2 |
228 | \& use metaclass 'Moose::Meta::Class' => |
229 | \& ( instance_metaclass => 'My::Meta::Instance' ); |
230 | .Ve |
231 | .PP |
232 | .Vb 1 |
233 | \& use Moose; |
234 | .Ve |
235 | .PP |
236 | .Vb 4 |
237 | \& has 'name' => ( |
238 | \& is => 'rw', |
239 | \& isa => 'Str', |
240 | \& ); |
241 | .Ve |
242 | .PP |
243 | .Vb 4 |
244 | \& has 'email' => ( |
245 | \& is => 'rw', |
246 | \& isa => 'Str', |
247 | \& ); |
248 | .Ve |
249 | .SH "DESCRIPTION" |
250 | .IX Header "DESCRIPTION" |
251 | This recipe shows how to build your own meta\-instance. The meta |
252 | instance is the metaclass that creates object instances and helps |
253 | manages access to attribute slots. |
254 | .PP |
255 | In this example, we're creating a meta-instance that is based on a |
256 | glob reference rather than a hash reference. This example is largely |
257 | based on the Piotr Roszatycki's MooseX::GlobRef module. |
258 | .PP |
259 | Our class is a subclass of Moose::Meta::Instance, which creates |
260 | hash reference based objects. We need to override all the methods |
261 | which make assumptions about the object's data structure. |
262 | .PP |
263 | The first method we override is \f(CW\*(C`create_instance\*(C'\fR: |
264 | .PP |
265 | .Vb 5 |
266 | \& sub create_instance { |
267 | \& my $self = shift; |
268 | \& my $sym = gensym(); |
269 | \& bless $sym, $self\->_class_name; |
270 | \& } |
271 | .Ve |
272 | .PP |
273 | This returns an glob reference which has been blessed into our |
274 | meta\-instance's associated class. |
275 | .PP |
276 | We also override \f(CW\*(C`clone_instance\*(C'\fR to create a new array reference: |
277 | .PP |
278 | .Vb 2 |
279 | \& sub clone_instance { |
280 | \& my ( $self, $instance ) = @_; |
281 | .Ve |
282 | .PP |
283 | .Vb 2 |
284 | \& my $new_sym = gensym(); |
285 | \& %{*$new_sym} = %{*$instance}; |
286 | .Ve |
287 | .PP |
288 | .Vb 2 |
289 | \& bless $new_sym, $self\->_class_name; |
290 | \& } |
291 | .Ve |
292 | .PP |
293 | After that, we have a series of methods which mediate access to the |
294 | object's slots (attributes are stored in \*(L"slots\*(R"). In the default |
295 | instance class, these expect the object to be a hash reference, but we |
296 | need to change this to expect a glob reference instead. |
297 | .PP |
298 | .Vb 4 |
299 | \& sub get_slot_value { |
300 | \& my ( $self, $instance, $slot_name ) = @_; |
301 | \& *$instance\->{$slot_name};; |
302 | \& } |
303 | .Ve |
304 | .PP |
305 | This level of indirection probably makes our instance class \fIslower\fR |
306 | than the default. However, when attribute access is inlined, this |
307 | lookup will be cached: |
308 | .PP |
309 | .Vb 4 |
310 | \& sub inline_create_instance { |
311 | \& my ( $self, $class_variable ) = @_; |
312 | \& return 'do { my $sym = Symbol::gensym(); bless $sym, ' . $class_variable . ' }'; |
313 | \& } |
314 | .Ve |
315 | .PP |
316 | The code snippet that the \f(CW\*(C`inline_slot_access\*(C'\fR method returns will |
317 | get \f(CW\*(C`eval\*(C'\fR'd once per attribute. |
318 | .PP |
319 | Finally, we use this meta-instance in our \f(CW\*(C`MyApp::User\*(C'\fR class: |
320 | .PP |
321 | .Vb 2 |
322 | \& use metaclass 'Moose::Meta::Class' => |
323 | \& ( instance_metaclass => 'My::Meta::Instance' ); |
324 | .Ve |
325 | .PP |
326 | We actually don't recommend the use of metaclass in most |
327 | cases. However, the other ways of using alternate metaclasses are more |
328 | complex, and would complicate our example code unnecessarily. |
329 | .SH "CONCLUSION" |
330 | .IX Header "CONCLUSION" |
331 | This recipe shows how to create your own meta-instance class. It's |
332 | unlikely that you'll need to do this yourself, but it's interesting to |
333 | take a peek at how Moose works under the hood. |
334 | .SH "SEE ALSO" |
335 | .IX Header "SEE ALSO" |
336 | There are a few meta-instance class extensions on \s-1CPAN:\s0 |
337 | .IP "* MooseX::Singleton" 4 |
338 | .IX Item "MooseX::Singleton" |
339 | This module extends the instance class in order to ensure that the |
340 | object is a singleton. The instance it uses is still a blessed hash |
341 | reference. |
342 | .IP "* MooseX::GlobRef" 4 |
343 | .IX Item "MooseX::GlobRef" |
344 | This module makes the instance a blessed glob reference. This lets you |
345 | use a handle as an object instance. |
346 | .SH "AUTHOR" |
347 | .IX Header "AUTHOR" |
348 | Dave Rolsky <autarch@urth.org> |
349 | .SH "COPYRIGHT AND LICENSE" |
350 | .IX Header "COPYRIGHT AND LICENSE" |
351 | Copyright 2006\-2009 by Infinity Interactive, Inc. |
352 | .PP |
353 | <http://www.iinteractive.com> |
354 | .PP |
355 | This library is free software; you can redistribute it and/or modify |
356 | it under the same terms as Perl itself. |