Volks,
am I just slow or what?
I liked david's illustration yesterday, and dashed off
this morning to code up the illustration about overridden
method - on the specific order of Connie's original concern,
so I had three packages A, B1, C - { base is to the left }.
So B1's overriding of A's return_hash() method did the
and C's overriding of B1 worked smothely with a variation
on the basic:
sub return_hash {
my ($self) = shift;
my $hash = $self->SUPER::return_hash();
$hash->{B} = 'B2';
return($hash);
}
but when I went to make the method in B1 that C would
inherit to display the inheritence chain, I had thought
I could likewise get away with the 'SUPER' trick a la
sub parent_chain {
my ($me) = @_;
my @generations = ref($me);
for my $parent ( @{$me->child_of()} ) {
#
# check that my 'SUPER' can parent_chain()
#
if ( my $sub_ref = $me->SUPER::can('parent_chain')) {
# this is line #83
my $grand_parents = $me->SUPER::parent_chain();
push(@generations, $_) for (@$grand_parents);
} else {
push(@generations, $parent);
}
}
return(\@generations);
}
only to get the error message on the order of
File "B1.pm"; Line 84:
Can't locate object method "parent_chain" via package "B1"
and then it HIT ME!
Smack! - and this is where I need some help making sure
that my 'explanaition' matches the 'real answer'...
package C inherited that method from B1, B1 did not over-ride that
method - so
a) the fact that the $me there is a blessed reference
to the Class C
b) there exists no over-ridden method in the super-class
of B1 that can be called - and that $sub_ref - which
is the address of this method ... while 'true' in the
sense that it is NOT an undefined value - did not majikally
"jump" where I had mistakenly thought it should...
So i re-wrote that as:
sub parent_chain {
my ($me) = @_;
my @generations = ref($me);
for my $parent ( @{$me->child_of()} ) {
if ( UNIVERSAL::can($parent, 'parent_chain' )) {
push (@generations, $_ )
for @{$parent->new->parent_chain()} ;
} else {
push(@generations, $parent);
}
}
return(\@generations);
} # end of parent_chain
Which expressly asks IF my Parent Class can do that method,
then we do the usual autonomous object method...
so that the simple demo code
#!/usr/bin/perl -w
use strict;
use C ; # we find it because @INC includes "."
my $c = new C;
my $family_tree = $c->parent_chain();
print "Iam - ", shift @$family_tree ," :\n ";
while ( my $Iam = shift @$family_tree) {
print "Which is a Child of - $Iam :\n ";
}
happily generates:
Iam - C :
Which is a Child of - B1 :
Which is a Child of - A :
Hence one should only use SUPER in a method if
a) the method itself is overriding an inherited method
b) you have a clue that in multiple class inheritences
you will find the one you really want?
ciao
drieux
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