in reply to sv_derived_from vs. sub ISA

Should the XS implementation give the (overridable) isa method the precedence?

Only if you want Perl's OO to keep working. In all other cases -- every one -- Perl calls overridden methods which optionally call super methods.

(Modern versions of UNIVERSAL explicitly recommend against calling UNIVERSAL::isa directly.)

Replies are listed 'Best First'.
Re^2: sv_derived_from vs. sub ISA
by rehsack (Sexton) on Apr 06, 2009 at 06:42 UTC
    Should the XS implementation give the (overridable) isa method the precedence?

    Only if you want Perl's OO to keep working. In all other cases -- every one -- Perl calls overridden methods which optionally call super methods.

    (Modern versions of UNIVERSAL explicitly recommend against calling UNIVERSAL::isa directly.)

    So if I understand you correctly, it's recommented to do: 
    package A;

sub foo {};

package B;

sub bar {};

package C;

use vars qw(@ISA);
@ISA = qw(B);

sub foo {};
sub isa {
  return $_[1] eq 'A' or $_[0]->SUPER::isa(@_);
}

    [download]
    against: 
    package A;

sub foo {};

package B;

sub bar {};

package C;

use vars qw(@ISA);
@ISA = qw(A B);

    [download]
    Or at least it's an allowed and wanted to work way? Further: It's allowed and wanted to work that: 
    package C;

use vars qw(@ISA);
@ISA = qw(B);

sub foo {};
sub isa {
  return $_[1] eq 'A';
}

    [download]
    To prevent, C is no B?
[reply]
[d/l]
[select]

      Yes, that's allowable. It's probably not a good idea from the OO design standpoint, but it's allowable.

      (In your first case, I'd override UNIVERSAL::DOES instead, but that's a 5.10 feature.)

[reply]
[d/l]

In Section Seekers of Perl Wisdom