Re^4: 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;
[download]

# Module2.pm
# ==========

package Module2;
use Exporter ();
our $VERSION = '2.0';
our @ISA = 'Exporter';
1;
[download]

# 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"); }
[download]

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.
[download]

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;
[download]

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;
[download]

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.

Comment on Re^4: Finding version of a Perl module Select or Download Code

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.	[reply] [d/l] [select]
Re^6: Finding version of a Perl module by ikegami (Patriarch) on Sep 09, 2005 at 15:37 UTC
That's interesting! My apologies.	[reply]


P is for Practical
	PerlMonks