Re: Foo is not a Bar, why?

[PodMaster]

in reply to Foo is not a Bar, why?

And that be the argument for slaping the @ISA assignment in a BEGIN block

my $foo = Foo->new;
print "foo is".($foo->isa( 'Bar' ) ? '' : ' _not_')." a Bar\n";

package Bar;

package Foo;
BEGIN { @Foo::ISA = qw(Bar); }
sub new { bless {},shift }
__END__
foo is a Bar

[Mr_Person]

Or using the nicer-looking use base. It will complain that the Bar package is empty, so I put a sub in it, but then it works fine.

my $foo = Foo->new;
print "foo is".($foo->isa( 'Bar' ) ? '' : ' _not_')." a Bar\n";

package Bar;
sub null {}

package Foo;
use base Bar;
sub new { bless {},shift }

[liz]

Hmmm... which version of Perl are you using? I don't need a sub null {} inside Bar to get it to run as expected.

Slaven Rezic pointed out (on p5p) the use of base.pm as an alternative. I assumed it would always require an external file: apparently it doesn't do that (anymore, anyway, I seem to remember that at one point it did. But I am probably wrong about that).

What I don't like about base.pm is the extra stuff about fields. Have you ever looked under the hood of base.pm? Yuck!

Liz

Update:
Argh. The reason I didn't get any errors about the empty Bar package, was that I actually had a Bar.pm as an external file hanging around from some previous testing. So yes, you need something in there, not necessarily a sub null {} though, a $VERSION = '0.01' also does the trick. Thanks to Mr. Person for his perseverance proving me wrong in this matter.

[PodMaster]

It's one of the reasons I wrote vars::i

my $foo = Foo->new;
print "foo is".($foo->isa( 'Bar' ) ? '' : ' _not_')." a Bar\n";

package Bar;
sub null {}

package Foo;
use vars::i qw[ @ISA Bar ];
sub new { bless {},shift }
__END__
foo is a Bar

[Mr_Person]

I'm on Perl 5.6.1, and it gives me:

Base class package "Bar" is empty.
        (Perhaps you need to 'use' the module which defines that packa
+ge first.) at test.pl line 10
BEGIN failed--compilation aborted at test.pl line 10.

If I don't put the sub null {} in, but that wouldn't generally be a problem for a real situation because you'd almost always have something in the package.