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

I just wrote this little module. The problem it tries to solve is the following.

I have a set of packages, each of which specifies a part of the behaviour I need. The idea is to be able to exchange one specification with another (for those who know, I'm translating an ASM specification).

I wrote the subs in the packages to be used as methods, and one of the packages defines new, but this is not really relevant...

What I can do is something like:

 package a;
 sub sa { return 1 }
 sub sb { return 2 }

 package b;
 sub sb { return 3 }

 package main;
 use Class::Merge qw(b a) => 'c';

 $r= c->sb();  # returns 3

[download]

This, coupled with NEXT, gets me the result I need.

Now I ask:

Oh, the whole module boils down to:

sub import {
  my $dest=pop;
  shift;
  eval <<"EOF";
package $dest;
\@${dest}::ISA=qw(@_);
EOF
}

[download]

Replies are listed 'Best First'.
(tye)Re: A module to merge packages
by tye (Sage) on Jun 26, 2002 at 14:18 UTC

    Does your module boil down to more than the following?    @c::ISA= qw( b a ); If not, perhaps a more thorough description is in order.

            - tye (but my friends call me "Tye")
[reply]
[d/l]

      Actually, no.

      It's just a fancy way to set that @ISA.

[reply]
•Re: A module to merge packages
by merlyn (Sage) on Jun 26, 2002 at 15:37 UTC
    Ya know, instead of: 
    use Class::Merge qw(b a) => 'c';

    [download]
    I'd just as soon write: 
    @C::ISA = qw(b a);

    [download]
    as it is shorter and clearer, and doesn't require me to install a separate module. And it's "use strict" savvy. {grin}

    -- Randal L. Schwartz, Perl hacker

[reply]
[d/l]
[select]
Re: A module to merge packages
by janx (Monk) on Jun 26, 2002 at 13:42 UTC
    Actually Schwern already has published something like that, but his version is based on randomness.

    You might call it Symbol::Merge.
    Or maybe even: Sub::Merge to keep in tradition with Simon Cozens' Sub::Versive.

    Kay

[reply]
Re: A module to merge packages
by Baboon (Acolyte) on Jun 26, 2002 at 13:43 UTC
    There is already a module Sex which does what you do, and it's available as ActiveState installation package, and also exists on CPAN, version 0.69

    Best wishes,
    I.R.Baboon.

[reply]
[d/l]

      I know of Schwern's Sex, but what the two modules do is different.

      My Merge creates a package whose @ISA is a list I specify.

      Sex creates a package by mixing up symbol table entries, both subs and variables, and (by the way) pushing the "parents" into the "child"'s @ISA.

      My first solution was a simplification of Sex (with less error checking, no schwernian messages, and no randomness), but it creates problem with classes, and makes it impossible to use NEXT to add functionality to a method, in something like:

      package a;
sub method {
 my $self=shift;
 # do something
}

package b;
use NEXT;
sub method {
 my $self=shift;
 # do something before
 $self->NEXT::method(@_); # do the normal stuff
 # do something after
}

package main;
require a;require b;
use Merge qw(b a)=>'c';

$c=new c;$c->method; # will call "b"'s implemetation, which will call 
+"a"'s via NEXT

      [download]
[reply]
[d/l]

Back to Seekers of Perl Wisdom