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10 | # to go back to "/" no matter how myfun exits: |
10 | # to go back to "/" no matter how myfun exits: |
11 | sub myfun { |
11 | sub myfun { |
12 | scope_guard { chdir "/" }; |
12 | scope_guard { chdir "/" }; |
13 | chdir "/etc"; |
13 | chdir "/etc"; |
14 | |
14 | |
15 | call_function_that_might_die_or_other_fun_stuff; |
15 | code_that_might_die_or_does_other_fun_stuff; |
16 | } |
16 | } |
17 | |
17 | |
18 | =head1 DESCRIPTION |
18 | =head1 DESCRIPTION |
19 | |
19 | |
20 | This module implements so-called "guards". A guard is something (usually |
20 | This module implements so-called "guards". A guard is something (usually |
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37 | package Guard; |
37 | package Guard; |
38 | |
38 | |
39 | no warnings; |
39 | no warnings; |
40 | |
40 | |
41 | BEGIN { |
41 | BEGIN { |
42 | $VERSION = '0.5'; |
42 | $VERSION = '1.02'; |
43 | @ISA = qw(Exporter); |
43 | @ISA = qw(Exporter); |
44 | @EXPORT = qw(guard scope_guard); |
44 | @EXPORT = qw(guard scope_guard); |
45 | |
45 | |
46 | require Exporter; |
46 | require Exporter; |
47 | |
47 | |
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162 | all, they are usually used to clean up after such exceptions. However, if |
162 | all, they are usually used to clean up after such exceptions. However, if |
163 | something truly exceptional is happening, a guard block should be allowed |
163 | something truly exceptional is happening, a guard block should be allowed |
164 | to die. Also, programming errors are a large source of exceptions, and the |
164 | to die. Also, programming errors are a large source of exceptions, and the |
165 | programmer certainly wants to know about those. |
165 | programmer certainly wants to know about those. |
166 | |
166 | |
167 | Since in most cases, the block executing when the guard gets executes does |
167 | Since in most cases, the block executing when the guard gets executed does |
168 | not know or does not care about the guard blocks, it makes little sense to |
168 | not know or does not care about the guard blocks, it makes little sense to |
169 | let containing code handle the exception. |
169 | let containing code handle the exception. |
170 | |
170 | |
171 | Therefore, whenever a guard block throws an exception, it will be caught, |
171 | Therefore, whenever a guard block throws an exception, it will be caught, |
172 | and this module will call the code reference stored in C<$Guard::DIED> |
172 | followed by calling the code reference stored in C<$Guard::DIED> (with |
173 | (with C<$@> set to the actual exception), which is similar to how most |
173 | C<$@> set to the actual exception), which is similar to how most event |
174 | event loops handle this case. |
174 | loops handle this case. |
175 | |
175 | |
176 | The default for C<$Guard::DIED> is to call C<warn "$@">. |
176 | The default for C<$Guard::DIED> is to call C<warn "$@">. |
177 | |
177 | |
178 | The C<$@> variable will be restored to its value before the guard call in |
178 | The C<$@> variable will be restored to its value before the guard call in |
179 | all cases, so guards will not disturb C<$@> in any way. |
179 | all cases, so guards will not disturb C<$@> in any way. |
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189 | =head1 THANKS |
189 | =head1 THANKS |
190 | |
190 | |
191 | Thanks to Marco Maisenhelder, who reminded me of the C<$Guard::DIED> |
191 | Thanks to Marco Maisenhelder, who reminded me of the C<$Guard::DIED> |
192 | solution to the problem of exceptions. |
192 | solution to the problem of exceptions. |
193 | |
193 | |
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194 | =head1 SEE ALSO |
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195 | |
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196 | L<Scope::Guard> and L<Sub::ScopeFinalizer>, which actually implement |
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197 | dynamic, not scoped guards, and have a lot higher CPU, memory and typing |
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198 | overhead. |
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199 | |
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200 | L<Hook::Scope>, which has apparently never been finished and corrupts |
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201 | memory when used. |
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202 | |
194 | =cut |
203 | =cut |
195 | |
204 | |