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Postings from November 2003
# New Ticket Created by Tom Phoenix
# Please include the string: [perl #24460]
# in the subject line of all future correspondence about this issue.
# <URL: http://rt.perl.org/rt2/Ticket/Display.html?id=24460 >
This doc patch may be added to perlmod, if it succeds in its goal of
making the order of execution clearer.
--Tom Phoenix
- - - - - - - - - - - - - - - - - -
--- ./perl-5.8.2-orig/pod/perlmod.pod Tue Sep 30 10:11:48 2003
+++ ./perl-5.8.2/pod/perlmod.pod Mon Nov 10 08:56:10 2003
@@ -257,7 +257,8 @@
Four special subroutines act as package constructors and destructors.
These are the C<BEGIN>, C<CHECK>, C<INIT>, and C<END> routines. The
-C<sub> is optional for these routines.
+C<sub> is optional for these routines. Try the B<begincheck> program, at
+the end of this section, to see them in action.
A C<BEGIN> subroutine is executed as soon as possible, that is, the moment
it is completely defined, even before the rest of the containing file
@@ -300,6 +301,35 @@
Both C<BEGIN> and C<CHECK> blocks are run when you use the B<-c>
switch for a compile-only syntax check, although your main code
is not.
+
+The B<begincheck> program makes it all clear, eventually:
+
+ #!/usr/bin/perl
+
+ # begincheck
+
+ print " 8. Ordinary code runs at runtime.\n";
+
+ END { print "14. So this is the end of the story.\n" }
+ INIT { print " 5. INIT blocks run FIFO just before runtime.\n" }
+ CHECK { print " 4. So this is the fourth line.\n" }
+
+ print " 9. It runs in order, of course.\n";
+
+ BEGIN { print " 1. BEGIN blocks run FIFO during compilation.\n" }
+ END { print "13. Read perlmod for the rest of the details.\n" }
+ CHECK { print " 3. CHECK blocks run LIFO at compilation's end.\n" }
+ INIT { print " 6. Run this again, using Perl's -c switch.\n" }
+
+ print "10. This is anti-obfuscated code.\n";
+
+ END { print "12. END blocks run LIFO at quitting time.\n" }
+ BEGIN { print " 2. So this line comes out second.\n" }
+ INIT { print " 7. You'll see the difference right away.\n" }
+
+ print "11. It merely _looks_ like it should be confusing.\n";
+
+ __END__
=head2 Perl Classes