in reply to Exporter (sometimes) doesn't seem to export if it's not first in @ISA

use Module;

  -and-

use Module qw( ... );

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are basically the same as 
BEGIN {
   require Module;
   Module->import();
}

  -and-

BEGIN {
   require Module;
   Module->import(qw( ... ));
}

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Your module doesn't have an import method, so the modules in @ISA are searched for one. Both CGI and Exporter have an import function, so the one that will be called will be controlled by the order of the classes in @ISA.

If you want Exporter's import, put Exporter early enough in @ISA or add the following to your module: 

{
   no warnings 'once';
   *import = \&Exporter::import;
}

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(For what it's worth, I've always thought Exporter's reliance on inheritance is dumb.)

Replies are listed 'Best First'.
Re^2: Exporter (sometimes) doesn't seem to export if it's not first in @ISA
by mcdave (Beadle) on Apr 15, 2010 at 17:28 UTC

    That's interesting and very clear. And it led me straight to the solution for my particular case about Class::DBI on the different machines. Both have version 3.0.17 of Class::DBI, but on Linux #1: 

    [mcdave@maia ~perl -MClass::DBI -MClass::ISA -e 'foreach $f (Class::IS
+A::super_path("Class::DBI")) { print join(" ", $f, ${"${f}::VERSION"}
+, "\n" ) ;}'
Class::DBI::__::Base -1, set by base.pm 
Class::Accessor 0.34 
Class::Data::Inheritable 0.08 
Ima::DBI 0.35 
[mcdave@maia ~]$ perl -MClass::DBI -e 'print Class::DBI->can("import")
+ ? "yes" : "no", "\n"'
yes

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    but on Linux #2: 
    [mcdave@trowel ~]$ perl -MClass::DBI -MClass::ISA -e 'foreach $f (Clas
+s::ISA::super_path("Class::DBI")) { print join(" ", $f, ${"${f}::VERS
+ION"}, "\n" ) ;}'
Class::DBI::__::Base -1, set by base.pm 
Class::Accessor 0.33 
Class::Data::Inheritable 0.08 
Ima::DBI 0.35 
[mcdave@trowel ~]$  perl -MClass::DBI -e 'if( Class::DBI->can("import"
+) ) { print "yes" } else { print "no" }; print "\n"'
no

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    So I conclude that the "difference" is in Class::Accessor!

    Thanks for your clear explanation

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