special $dbh can't error?

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

(re)Blessed minds,

Imagine the following code:

use DBI;
my $dbh=DBI->connect("dbi:mysql:hostname=localhost;database=somedb","u
+serok","passwdok");
bless $dbh, "My::Special::DBI::db";

print "can error: ", $dbh->can("error"),"\n";

package My::Special::DBI::db;
use base qw(DBI::db);

sub error {
   my $dbh=shift;
   return $dbh->errstr();
}
[download]

I would expect that in this code, the $dbh->can("error") returned a reference to My::Special::DBI::db::error.

However, undef is returned.

Can anyone explain me what sets my expections out of sync with reality?

For extra-information, I tested this with:

perl -v
This is perl, v5.8.7 built for x86_64-linux-gnu-thread-multi

perl -v
This is perl, v5.10.0 built for i486-linux-gnu-thread-multi
[download]

Thank you, everyone.

TheMage
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Re: special $dbh can't error? by Anonymous Monk on Oct 03, 2008 at 10:43 UTC
Can anyone explain me what sets my expections out of sync with reality? Probably because can isn't what you think it is. Try UNIVERSAL::can() use DBI; my $dbh=DBI->connect("dbi:SQLite:dbname=dbfile"); warn $dbh; print "can error: ", $dbh->can("error"),"\n"; print "UNIVERSAL::can((", UNIVERSAL::can($dbh,'error'),"\n"; eval {print $dbh->error('eeep');};warn $@ if $@; bless $dbh, "My::Special::DBI::db"; warn $dbh; print "can error: ", $dbh->can("error"),"\n"; print "UNIVERSAL::can((", UNIVERSAL::can($dbh,'error'),"\n"; eval {print $dbh->error('eeep');};warn $@ if $@; print "\n-----\n\n"; package My::Special::DBI::db; use base qw(DBI::db); sub error { my $dbh=shift; return $dbh->errstr(); } __END__ DBI::db=HASH(0x19b7f1c) at dbi.dbd.error.subclass.pl line 3. can error: UNIVERSAL::can(( Can't locate object method "error" via package "DBI::db" at dbi.dbd.er +ror.subclass.pl line 6. My::Special::DBI::db=HASH(0x19b7f1c) at dbi.dbd.error.subclass.pl line + 8. can error: UNIVERSAL::can((CODE(0x19978e4) ----- [download]	[reply] [d/l]
Re: special $dbh can't error? by jethro (Monsignor) on Oct 03, 2008 at 12:30 UTC
It seems 'can' is overriden by DBI and for it to know your method you would have to override it in turn.	[reply]
Re: special $dbh can't error? by massa (Hermit) on Oct 03, 2008 at 15:32 UTC
`base.pm` seems to have a bug; if you use `push @ISA, qw(DBI::db);` [download] instead of `use base qw(DBI::db);` [download] the thing starts to work... []s, HTH, Massa (κς,πμ,πλ)	[reply] [d/l] [select]