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129 | .\" ======================================================================== |
130 | .\" |
131 | .IX Title "PadWalker 3" |
132 | .TH PadWalker 3 "2009-06-26" "perl v5.8.7" "User Contributed Perl Documentation" |
133 | .SH "NAME" |
134 | PadWalker \- play with other peoples' lexical variables |
135 | .SH "SYNOPSIS" |
136 | .IX Header "SYNOPSIS" |
137 | .Vb 2 |
138 | \& use PadWalker qw(peek_my peek_our peek_sub closed_over); |
139 | \& ... |
140 | .Ve |
141 | .SH "DESCRIPTION" |
142 | .IX Header "DESCRIPTION" |
143 | PadWalker is a module which allows you to inspect (and even change!) |
144 | lexical variables in any subroutine which called you. It will only |
145 | show those variables which are in scope at the point of the call. |
146 | .PP |
147 | PadWalker is particularly useful for debugging. It's even |
148 | used by Perl's built-in debugger. (It can also be used |
149 | for evil, of course.) |
150 | .PP |
151 | I wouldn't recommend using PadWalker directly in production |
152 | code, but it's your call. Some of the modules that use |
153 | PadWalker internally are certainly safe for and useful |
154 | in production. |
155 | .IP "peek_my \s-1LEVEL\s0" 4 |
156 | .IX Item "peek_my LEVEL" |
157 | .PD 0 |
158 | .IP "peek_our \s-1LEVEL\s0" 4 |
159 | .IX Item "peek_our LEVEL" |
160 | .PD |
161 | The \s-1LEVEL\s0 argument is interpreted just like the argument to \f(CW\*(C`caller\*(C'\fR. |
162 | So \f(CWpeek_my(0)\fR returns a reference to a hash of all the \f(CW\*(C`my\*(C'\fR |
163 | variables that are currently in scope; |
164 | \&\f(CWpeek_my(1)\fR returns a reference to a hash of all the \f(CW\*(C`my\*(C'\fR |
165 | variables that are in scope at the point where the current |
166 | sub was called, and so on. |
167 | .Sp |
168 | \&\f(CW\*(C`peek_our\*(C'\fR works in the same way, except that it lists |
169 | the \f(CW\*(C`our\*(C'\fR variables rather than the \f(CW\*(C`my\*(C'\fR variables. |
170 | .Sp |
171 | The hash associates each variable name with a reference |
172 | to its value. The variable names include the sigil, so |
173 | the variable \f(CW$x\fR is represented by the string '$x'. |
174 | .Sp |
175 | For example: |
176 | .Sp |
177 | .Vb 3 |
178 | \& my $x = 12; |
179 | \& my $h = peek_my (0); |
180 | \& ${$h\->{'$x'}}++; |
181 | .Ve |
182 | .Sp |
183 | .Vb 1 |
184 | \& print $x; # prints 13 |
185 | .Ve |
186 | .Sp |
187 | Or a more complex example: |
188 | .Sp |
189 | .Vb 4 |
190 | \& sub increment_my_x { |
191 | \& my $h = peek_my (1); |
192 | \& ${$h\->{'$x'}}++; |
193 | \& } |
194 | .Ve |
195 | .Sp |
196 | .Vb 3 |
197 | \& my $x=5; |
198 | \& increment_my_x; |
199 | \& print $x; # prints 6 |
200 | .Ve |
201 | .IP "peek_sub \s-1SUB\s0" 4 |
202 | .IX Item "peek_sub SUB" |
203 | The \f(CW\*(C`peek_sub\*(C'\fR routine takes a coderef as its argument, and returns a hash |
204 | of the \f(CW\*(C`my\*(C'\fR variables used in that sub. The values will usually be undefined |
205 | unless the sub is in use (i.e. in the call\-chain) at the time. On the other |
206 | hand: |
207 | .Sp |
208 | .Vb 3 |
209 | \& my $x = "Hello!"; |
210 | \& my $r = peek_sub(sub {$x})\->{'$x'}; |
211 | \& print "$$r\en"; # prints 'Hello!' |
212 | .Ve |
213 | .Sp |
214 | If the sub defines several \f(CW\*(C`my\*(C'\fR variables with the same name, you'll get the |
215 | last one. I don't know of any use for \f(CW\*(C`peek_sub\*(C'\fR that isn't broken as a result |
216 | of this, and it will probably be deprecated in a future version in favour of |
217 | some alternative interface. |
218 | .IP "closed_over \s-1SUB\s0" 4 |
219 | .IX Item "closed_over SUB" |
220 | \&\f(CW\*(C`closed_over\*(C'\fR is similar to \f(CW\*(C`peek_sub\*(C'\fR, except that it only lists |
221 | the \f(CW\*(C`my\*(C'\fR variables which are used in the subroutine but defined outside: |
222 | in other words, the variables which it closes over. This \fIdoes\fR have |
223 | reasonable uses: see Data::Dump::Streamer, for example (a future version |
224 | of which may in fact use \f(CW\*(C`closed_over\*(C'\fR). |
225 | .IP "set_closed_over \s-1SUB\s0, \s-1HASH_REF\s0" 4 |
226 | .IX Item "set_closed_over SUB, HASH_REF" |
227 | \&\f(CW\*(C`set_closed_over\*(C'\fR reassigns the pad variables that are closed over by the subroutine. |
228 | .Sp |
229 | The second argument is a hash of references, much like the one returned from \f(CW\*(C`closed_over\*(C'\fR. |
230 | .IP "var_name \s-1LEVEL\s0, \s-1VAR_REF\s0" 4 |
231 | .IX Item "var_name LEVEL, VAR_REF" |
232 | .PD 0 |
233 | .IP "var_name \s-1SUB\s0, \s-1VAR_REF\s0" 4 |
234 | .IX Item "var_name SUB, VAR_REF" |
235 | .PD |
236 | \&\f(CW\*(C`var_name(sub, var_ref)\*(C'\fR returns the name of the variable referred to |
237 | by \f(CW\*(C`var_ref\*(C'\fR, provided it is a \f(CW\*(C`my\*(C'\fR variable used in the sub. The \f(CW\*(C`sub\*(C'\fR |
238 | parameter can be either a \s-1CODE\s0 reference or a number. If it's a number, |
239 | it's treated the same way as the argument to \f(CW\*(C`peek_my\*(C'\fR. |
240 | .Sp |
241 | For example, |
242 | .Sp |
243 | .Vb 2 |
244 | \& my $foo; |
245 | \& print var_name(0, \e$foo); # prints '$foo' |
246 | .Ve |
247 | .Sp |
248 | .Vb 4 |
249 | \& sub my_name { |
250 | \& return var_name(1, shift); |
251 | \& } |
252 | \& print my_name(\e$foo); # ditto |
253 | .Ve |
254 | .SH "AUTHOR" |
255 | .IX Header "AUTHOR" |
256 | Robin Houston <robin@cpan.org> |
257 | .PP |
258 | With contributions from Richard Soberberg, Jesse Luehrs and |
259 | Yuval Kogman, bug-spotting from Peter Scott, Dave Mitchell and |
260 | Goro Fuji, and suggestions from demerphq. |
261 | .SH "SEE ALSO" |
262 | .IX Header "SEE ALSO" |
263 | Devel::LexAlias, Devel::Caller, Sub::Parameters |
264 | .SH "COPYRIGHT" |
265 | .IX Header "COPYRIGHT" |
266 | Copyright (c) 2000\-2009, Robin Houston. All Rights Reserved. |
267 | This module is free software. It may be used, redistributed |
268 | and/or modified under the same terms as Perl itself. |