in reply to Re: opinions on the best way to inherit class data
in thread opinions on the best way to inherit class data

Thanks for the reply, chromatic.

i think i was perhaps not clear enough about my definition of 'class data', as opposed to 'class defaults', which i believe your response addresses. my apologies.

some typical 'class data' for example might be:

# base class
package AbstractMyClass;

my $_Class_Count = 0;

sub new
{
    my $class = shift;
    my $this = bless( {}, $class );

    ref($this) && $_Class_Count++;
    return $this;    
}

package MyClass;
@MyClass::ISA = ('AbstractMyClass');

sub new
{    
    my $class = shift;
    my $this = $class::SUPER->new( @_ );
    # this class' init...
    
    return $this;
}

[download]

if i were to use the code...

use AbstractMyClass;
use MyClass;

my $amc = new AbstractMyClass ();
my $mc = new MyClass ();

[download]

...$AbstractMyClass::_Class_Count would be 2, whereas i would have really liked $AbstractMyClass::_Class_Count to be 1, and $MyClass::_Class_Count to be 1. Probably a bad example of the essence of my original question, but nevertheless illustrative of what i am terming 'class data'. thanks, matt aka d_i_r_t_y, since 'zero cool' was taken... ;-)

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RE: RE: Re: opinions on the best way to inherit class data
by chromatic (Archbishop) on Aug 23, 2000 at 08:33 UTC
    Oh, that's what you mean! Here's a sneaky way to do it: 
    #!/usr/bin/perl -w

use strict;

package Superclass;

use vars qw ( $AUTOLOAD );

my $classdata = qq|
{
    my \$self = shift;
    my \$invocations = 0;
    sub _increase {
        \$invocations++;
    }
    sub number {
        return \$invocations;
    }
}|;

sub new {
    my $class = shift;
    if ($class ne __PACKAGE__) {    # he he he
        eval qq|package $class; $classdata |;
    }
    my $self = {};
    bless($self, $class);
    $self->_increase();
    return $self;
}

eval $classdata;

package Subclass;

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

package main;

print Superclass->number();
my $one = Superclass->new();
print $one->number();
print Subclass->number();
my $two = Subclass->new();
print $two->number();

    [download]
    If your superclass is in a different module, you can play around with the import subroutine and do it a bit more cleanly.

    This technique has the unfortunate effect of making Subclass->number() return 1 before you create any instance of Subclass. (Inheritance... oh well.)

[reply]
[d/l]

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