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Comparing Guard/Guard.pm (file contents):
Revision 1.13 by root, Sat Dec 13 19:14:58 2008 UTC vs.
Revision 1.21 by root, Sun Jul 19 05:44:10 2009 UTC

… …
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
18 # create an object that, when the last reference to it is gone,
19 # invokes the given codeblock:
20 my $guard = guard { print "destroyed!\n" };
21 undef $guard; # probably destroyed here
17 22
18=head1 DESCRIPTION 23=head1 DESCRIPTION
19 24
20This module implements so-called "guards". A guard is something (usually 25This module implements so-called "guards". A guard is something (usually
21an object) that "guards" a resource, ensuring that it is cleaned up when 26an object) that "guards" a resource, ensuring that it is cleaned up when
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37package Guard; 42package Guard;
38 43
39no warnings; 44no warnings;
40 45
41BEGIN { 46BEGIN {
42 $VERSION = '0.5'; 47 $VERSION = '1.021';
43 @ISA = qw(Exporter); 48 @ISA = qw(Exporter);
44 @EXPORT = qw(guard scope_guard); 49 @EXPORT = qw(guard scope_guard);
45 50
46 require Exporter; 51 require Exporter;
47 52
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162all, they are usually used to clean up after such exceptions. However, if 167all, they are usually used to clean up after such exceptions. However, if
163something truly exceptional is happening, a guard block should be allowed 168something truly exceptional is happening, a guard block should be allowed
164to die. Also, programming errors are a large source of exceptions, and the 169to die. Also, programming errors are a large source of exceptions, and the
165programmer certainly wants to know about those. 170programmer certainly wants to know about those.
166 171
167Since in most cases, the block executing when the guard gets executes does 172Since in most cases, the block executing when the guard gets executed does
168not know or does not care about the guard blocks, it makes little sense to 173not know or does not care about the guard blocks, it makes little sense to
169let containing code handle the exception. 174let containing code handle the exception.
170 175
171Therefore, whenever a guard block throws an exception, it will be caught, 176Therefore, whenever a guard block throws an exception, it will be caught,
172and this module will call the code reference stored in C<$Guard::DIED> 177followed 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 178C<$@> set to the actual exception), which is similar to how most event
174event loops handle this case. 179loops handle this case.
175 180
176The default for C<$Guard::DIED> is to call C<warn "$@">. 181The default for C<$Guard::DIED> is to call C<warn "$@">.
177 182
178The C<$@> variable will be restored to its value before the guard call in 183The C<$@> variable will be restored to its value before the guard call in
179all cases, so guards will not disturb C<$@> in any way. 184all cases, so guards will not disturb C<$@> in any way.
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189=head1 THANKS 194=head1 THANKS
190 195
191Thanks to Marco Maisenhelder, who reminded me of the C<$Guard::DIED> 196Thanks to Marco Maisenhelder, who reminded me of the C<$Guard::DIED>
192solution to the problem of exceptions. 197solution to the problem of exceptions.
193 198
199=head1 SEE ALSO
200
201L<Scope::Guard> and L<Sub::ScopeFinalizer>, which actually implement
202dynamic, not scoped guards, and have a lot higher CPU, memory and typing
203overhead.
204
205L<Hook::Scope>, which has apparently never been finished and corrupts
206memory when used.
207
194=cut 208=cut
195 209

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