On Mon, Sep 18, 2000 at 05:49:28AM -0000, Perl6 RFC Librarian wrote:
> Here's where the problem lies. Even though we now have a subclass
> of Frog, the Forest class is still referencing the original Frog
> class and not Frog::Japanese.
The DBI has this very problem! DBI->connect() returns DBI::db
objects, DBI->prepare() returns DBI::st. If you want to override the
behavior for statement handles and connections, its not enough to just
subclass DBI::st and DBI::db, you must also subclass DBI and override
connect() and prepare() (and hope DBI doesn't use DBI::st or DBI::db
anywhere else.)
DBI->init_rootclass() is a fairly hairy workaround to this problem.
It works like this:
package Ima::DBI::db;
@ISA = qw(DBI::db);
package Ima::DBI::st;
@ISA = qw(DBI::st);
package Ima::DBI;
use base qw(DBI);
Ima::DBI->init_rootclass;
# $dbh is an Ima::DBI::db object, $sth is an Ima::DBI::st
$dbh = Ima::DBI->connect(...);
$sth = $dbh->prepare(...);
Ima::DBI->init_rootclass() informs the DBI that Ima::DBI is a subclass
and that Ima::DBI::db and Ima::DBI::st objects should be used. It
does this by just appending '::db' onto the classname, which means the
names of the classes are fixed. A Bad Thing.
[From DBI->connect()]
# XXX this is inelegant but practical in the short term, sigh.
if ($installed_rootclass{$class}) {
$dbh->{RootClass} = $class;
bless $dbh => $class.'::db';
my ($outer, $inner) = DBI::_handles($dbh);
bless $inner => $class.'::db';
}
It works, but to quote Tim Bunce there... *sigh*.
So anyhow, yes, this is a big, icky problem.
--
Michael G Schwern http://www.pobox.com/~schwern/ [EMAIL PROTECTED]
Just Another Stupid Consultant Perl6 Kwalitee Ashuranse
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