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Postings from February 2004
Something weird happens if a constant gets an undef value and then used inside
to define a lexical which is then used in the conditional. Consider this code:
#/tmp/constants
use strict;
use warnings;
use constant CONST => eval { require notthere } && 1;
#use constant CONST => undef;
my $switch = 0;
$switch++ if CONST;
$switch-- if $switch;
/tmp> perl /tmp/constant
Useless use of a constant in void context at /tmp/constant line 8.
use constant CONST => undef;
has the same (bad) effect.
use constant CONST => 0;
works just fine.
I have had this problem trying to do:
use constant IS_MOD_PERL_2_BUILD =>
eval { require mod_perl && $mod_perl::VERSION >= 1.99 } &&
require Apache::Build && Apache::Build::IS_MOD_PERL_BUILD();
which gets an 'undef' when eval fails. so undef comes from:
use constant CONST => eval { die } && 1;
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Stas Bekman JAm_pH ------> Just Another mod_perl Hacker
http://stason.org/ mod_perl Guide ---> http://perl.apache.org
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