Where is the @ISA array?

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

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Re: Where is the @ISA array? by ikegami (Patriarch) on Jan 21, 2009 at 15:18 UTC
`@__PACKAGE__::ISA` means `@ISA` in the package "`__PACKAGE__`", not the current package. `use strict; use warnings; use base 'CGI'; print "@main::ISA\n"; # CGI our @ISA; print "@ISA\n"; # CGI my @ourISA = do { no strict 'refs'; @{__PACKAGE__ . '::ISA'} }; print "@ourISA\n"; # CGI` [download] I wouldn't use base. It's even been obsoleted with parent in newer versions of Perl.	[reply] [d/l] [select]
Re^2: Where is the @ISA array? by metaperl (Curate) on Jan 21, 2009 at 15:37 UTC
@__PACKAGE__::ISA means @ISA in the package "__PACKAGE__", not the current package. oh, so only with `__PACKAGE__->` do I get the current package placed there?	[reply] [d/l]
Re^3: Where is the @ISA array? by ikegami (Patriarch) on Jan 21, 2009 at 15:53 UTC
No, my post shows it being used elsewhere. And here's another: `$ perl -le'print __PACKAGE__' main` [download] You wouldn't expect `@time::ISA` to mean `@1232553153::ISA`. Same goes for `__PACKAGE__`. It's a built-in function like `time`. `$ perl -le'print CORE::__PACKAGE__' main` [download] Update: I can override it `$ perl -wle'BEGIN { *CORE::GLOBAL::__PACKAGE__ = sub () { "abc" }; } p +rint __PACKAGE__' abc` [download] but I can't call `prototype` on it `$ perl -wle'print prototype "CORE::__PACKAGE__"' Can't find an opnumber for "__PACKAGE__" at -e line 1.` [download] so it's not quite the same as other built-ins. That's probably the only difference.	[reply] [d/l] [select]
Re^2: Where is the @ISA array? by Anonymous Monk on Jan 22, 2009 at 00:01 UTC
Gosh. I didn't know about `parent`. What was wrong with `base`?	[reply] [d/l] [select]
Re^3: Where is the @ISA array? by ikegami (Patriarch) on Jan 22, 2009 at 05:39 UTC
It handles load failures badly.	[reply]
Re^4: Where is the @ISA array? by Anonymous Monk on Jan 22, 2009 at 13:31 UTC
Re^5: Where is the @ISA array? by Corion (Patriarch) on Jan 22, 2009 at 13:40 UTC
Some notes below your chosen depth have not been shown here
Re^5: Where is the @ISA array? by ikegami (Patriarch) on Jan 22, 2009 at 14:02 UTC
Re: Where is the @ISA array? by Corion (Patriarch) on Jan 21, 2009 at 15:17 UTC
`__PACKAGE__` is taken verbatim and not interpolated like you seem to think it would be. So you're looking at two different variables, `@{"__PACKAGE__::ISA"}` and `@{"metaperl::ISA"}`. Why aren't you simply printing out `@ISA`? Doing `__PACKAGE__` gymnastics just to get at variables seems a little roundabout to me.	[reply] [d/l] [select]
Re^2: Where is the @ISA array? by metaperl (Curate) on Jan 21, 2009 at 15:34 UTC
Why aren't you simply printing out @ISA? `@ISA` is a package variable. I am using strict. So I have to package qualify it. Doing __PACKAGE__ gymnastics just to get at variables seems a little roundabout to me. How would you do it?	[reply] [d/l]
Re^3: Where is the @ISA array? by Corion (Patriarch) on Jan 21, 2009 at 15:37 UTC
Simply `use vars '@ISA';`. There is no need to use fully qualified names. In fact, using fully qualified names removes the protection that `strict` buys you.	[reply] [d/l] [select]
Re^3: Where is the @ISA array? by JavaFan (Canon) on Jan 21, 2009 at 17:09 UTC
`print our @ISA`	[reply]
Re: Where is the @ISA array? by jeffa (Bishop) on Jan 21, 2009 at 15:16 UTC
Interesting. I don't have an answer per sey ... but this test seemed to work for me: `use strict; use warnings; my $bar = bar->new; $bar->foo; package foo; sub new { return bless {}, shift } package bar; use base qw( foo ); use Data::Dumper; sub new { return bless {}, shift } sub foo { print Dumper \@INC }` [download] DOH! ... silly /me -- of course that works ... i typo'ed and used @INC, not @ISA --- that final method should have been: `sub foo { print Dumper @__PACKAGE__::ISA }` [download] Which is empty. :/ I give up. UPDATE round 2: That final method should have been: `sub foo { print Dumper @bar::ISA }` [download] Which does indeed yield the parent class. I am not sure why `use base` is no longer acceptable for Perl 5. It was supposed to replace the need to push to @ISA directly -- perhaps `use base` is not going to cut the mustard when roles and traits show up? 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]