Howto implement versions of object instances

pajout has asked for the wisdom of the Perl Monks concerning the following question:

Hi all,
I am interest in solution of version-dependant methods in object instances. My idea is that

my $instance1 = MyModule::new('1.0');
print $instance1->version();
#prints '1.0';
my $instance2 = MyModule::new('2.0');
print $instance2->version();
#prints '2.0';
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instances are of the same class, with the same methods formally, but with different subroutines (doing different things) realizing these methods.
My current solution is based on declarative global hashref $vers

package MyModule;
our $VERSION = '2.0';
our $vers = {'1.0'=>{__PACKAGE__.'::version'=>\&version_1_0},
             '2.0'=>{__PACKAGE__.'::version'=>\&version_2_0}};
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,blessing proper part of $vers

sub new {
  my $class = __PACKAGE__;
  my $version = shift || $VERSION;
  return bless({methods=>$$vers{$version}},$class);
}
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and on

sub AUTOLOAD {
  my $self = $_[0];
  return &{$$self{methods}{$AUTOLOAD}}(@_);
}
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But i feel that AUTOLOADing is dirty for that, I wish some solution without it. Please, have you some hints or criticisms?

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Re: Howto implement versions of object instances by Aristotle (Chancellor) on Nov 15, 2005 at 11:58 UTC
The only good option I can think of is to put your interfaces in `MyModule::V1_0` and `MyModule::V2_0`, respectively, and then bless your object into one of these packages. If that’s out of the question, you’ll need some way to hook into the method lookup, and the only way to do that is with AUTOLOAD. Okay, there’s another way, but it’s rather brutish: put the methods in different packages as outlined above, then iterate over their symbol tables, picking out the functions, and assign a to the same symbols in `MyModule` a stub function that routes the call to the right package’s method. Makeshifts last the longest.	[reply]
Re^2: Howto implement versions of object instances by pajout (Curate) on Nov 15, 2005 at 12:07 UTC
Thanks, my other ideas are strolling through very similar ways :)	[reply]
Re: Howto implement versions of object instances by jeffa (Bishop) on Nov 15, 2005 at 17:41 UTC
How about the Factory Pattern? Factory.pm `package Factory; use base qw( Class::Factory ); use Module_1; use Module_2; __PACKAGE__->add_factory_type('1.0' => 'Module_1'); __PACKAGE__->add_factory_type('2.0' => 'Module_2'); 1;` [download] Module_1.pm `package Module_1; sub new { bless {}, shift } sub init { shift } sub version { '1.0' } 1;` [download] Module_2.pm `package Module_2; sub new { bless {}, shift } sub init { shift } sub version { '2.0' } 1;` [download] And the driver: `#!/usr/bin/perl -l use Factory; print $_->version for Factory->new('1.0'), Factory->new('2.0'), ;` [download] jeffa L-LL-L--L-LL-L--L-LL-L-- -R--R-RR-R--R-RR-R--R-RR B--B--B--B--B--B--B--B-- H---H---H---H---H---H--- (the triplet paradiddle with high-hat)	[reply] [d/l] [select]
Re: Howto implement versions of object instances by ghenry (Vicar) on Nov 15, 2005 at 11:58 UTC
Is this for backward compatibility? Or to try and cover a bad interface design ;-) (no insult intended) Gavin. Walking the road to enlightenment... I found a penguin and a camel on the way..... Fancy a yourname@perl.me.uk? Just ask!!!	[reply]
Re^2: Howto implement versions of object instances by pajout (Curate) on Nov 17, 2005 at 12:14 UTC
And to try and cover a bad interface design, too :))) I am not an excellent developer and I am not a clairvoyant, so I sometimes create method with inaccurate args or inaccurate interpretation of args, for instance. And discussed trick gives me freedom to improve the interface in the next versions, without affecting applications using the current one.	[reply]
Re^2: Howto implement versions of object instances by pajout (Curate) on Nov 15, 2005 at 12:04 UTC
Backward compatibility :) I try to develop my mod_perl application framework, and I need coexistency of slightly different versions of it at the same apache, to support applications developed on different $VERSIONs.	[reply]
Re^3: Howto implement versions of object instances by perrin (Chancellor) on Nov 15, 2005 at 15:02 UTC
It would be much easier to run two separate mod_perl servers.	[reply]
Re^4: Howto implement versions of object instances by pajout (Curate) on Nov 15, 2005 at 15:16 UTC
Re^5: Howto implement versions of object instances by perrin (Chancellor) on Nov 15, 2005 at 17:12 UTC
Re: Howto implement versions of object instances by radiantmatrix (Parson) on Nov 15, 2005 at 16:26 UTC
Hm, I had a brainstorm, but not time to test it. Please correct me if any of this wouldn't work for your mod_perl issues (or if any of my assumptions are wrong). Perl traverses `@INC` in order: as soon as it finds a module that fits a `require` or `use` statement, it acts on that and stops looking. (IIRC). So, why not do this: `use lib 'my_modules/old_version'; use lib 'my_modules/new_version'; use MyModule '2.0'; #if you need version 2.` [download] In theory, Perl would find version 1.0 in 'my_modules/old_version', and because it doesn't match, would keep looking, finding 2.0 in 'my_modules/new_version'. If you didn't ask for version '2.0', you'd see the 1.0 version first and use that.As ikegami points out below, this approach is flawed because Perl has to find and load the module before it knows the version. However, it looks like I was heading down the right path, as his approach (inverting the order of the paths in `@INC`) does work. Please ++ his post if you have spare votes! ~~I don't really know that use $VER works exactly that way... as I said this is a brainstorm. Thoughts?~~ <-radiant.matrix-> A collection of thoughts and links from the minds of geeks The Code that can be seen is not the true Code "In any sufficiently large group of people, most are idiots" - Kaa's Law	[reply] [d/l] [select]
Re^2: Howto implement versions of object instances by ikegami (Patriarch) on Nov 15, 2005 at 18:03 UTC
That doesn't work `>type v1\AA.pm package AA; our $VERSION = 1.0; 1; >type v2\AA.pm package AA; our $VERSION = 2.0; 1; >type test.pl use lib qw( v1 v2 ); use AA 2; >perl test.pl AA version 2 required--this is only version 1 at test.pl line 4. BEGIN failed--compilation aborted at test.pl line 4.` [download] By the time Perl figures out the version of the module, the module has already been executed. It is therefore impossible for Perl to continue looking for other versions of the module. By the way, if you reverse the order of the libraries (i.e. `use lib qw( v2 v1 );`), version 2 will always be loaded.	[reply] [d/l] [select]
Re^3: Howto implement versions of object instances by pajout (Curate) on Nov 16, 2005 at 09:34 UTC
Ikegami, radiantmatrix, thanks for your effort. But I would stress that I need all instances of my objects in the same runtime, paralelly, without choosing of versions on lib-use-require-phase. Maybe I am not catching something important, but I think that your advices do not support such parallelism.	[reply]