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Re^4: Finding version of a Perl module

by ikegami (Pope)
on Sep 09, 2005 at 15:23 UTC ( #490603=note: print w/replies, xml ) Need Help??


in reply to Re^3: Finding version of a Perl module
in thread Finding version of a Perl module

Yes, but you need something to call UNIVERSAL::VERSION. Usually, that something is Exporter. Proof:
# Module1.pm # ========== package Module1; our $VERSION = '2.0'; 1;
# Module2.pm # ========== package Module2; use Exporter (); our $VERSION = '2.0'; our @ISA = 'Exporter'; 1;
# script.pl # ========= BEGIN { print("Loading Module1...\n"); } use Module1 '3.0'; BEGIN { print("Loaded.\n"); } BEGIN { print("Loading Module2...\n"); } use Module2 '3.0'; BEGIN { print("Loaded.\n"); }
output ====== Loading Module1... Loaded. Loading Module2... Module2 3.0 required--this is only version 2.0 (Module2.pm) at script. +pl line 6 BEGIN failed--compilation aborted at script.pl line 6.

Notice how the version passed to Module1 is completely ignored.


In writing this test, I also found errors in what I thought I knew.

1) *import = \&Exporter::import; doesn't work as well as I thought. My original Module2 gave a run-time error. It was:

package Module2; use Exporter (); our $VERSION = '2.0'; *import = \&Exporter::import; 1;

To fix without inheriting from Exporter, one needs to also import require_version:

package Module2; use Exporter (); our $VERSION = '2.0'; *import = \&Exporter::import; *require_version = \&Exporter::require_version; 1;

2) I always thought use Module 'maj.min' would make sure the major version is the same as the one in $VERSION, yet use Module2 '1.0' doesn't fail.

Replies are listed 'Best First'.
Re^5: Finding version of a Perl module
by itub (Priest) on Sep 09, 2005 at 15:34 UTC
    That's interesting. But if you say use Module1 3.0; (notice that the version number is not in quotes), then you get
    Loading Module1...
    Module1 version 3 required--this is only version 2.0 at version.pl line 4.
    BEGIN failed--compilation aborted at version.pl line 4.
    

    It seems that if you give a number, the version check is done by use, but if you give a string it is treated as the first argument to pass to import, in which case you do need exporter to handle it.

    I hadn't noticed because I always call use by giving the version numbers as numbers, not as strings.

      That's interesting! My apologies.

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