My goal is to add new functionality to Bit::Vector without changing its source code. My strategy has been to make my own class that inherits from Bit::Vector, but it is resisting my strategy.

How can I make inheritance work with Bit::Vector? If inheritance won't work, what approach should I use?

The error message I get is 'Modification of a read-only value attempted' when I try to re-bless the Bit::Vector. If I don't re-bless, I get a Bit::Vector where I expect an LFSR object.

Here is my attempt so far:
The stripped-down calling program:

use strict;
use warnings;
use diagnostics;
use LFSR;
 
my $nbits = 127;
my $t = new LFSR($nbits); # Inherited constructor
print ref($t),"\n";       # Shows it is a Bit::Vector, not an LFSR
 
# More proof that $t is a Bit::Vector
print $t->isa('Bit::Vector'),"\n";
print $t->isa('LFSR'),"\n";
 
# This line:
# bless $t, "LFSR";
# Causes this error:
#  'Modification of a read-only value attempted'
[download]

The stripped-down module:

package LFSR;
 
use strict;
use warnings;
use diagnostics;
 
use Bit::Vector;
our @ISA = qw(Bit::Vector);
 

# This also causes an error at the bless statement,
# so I have it commented out.
=pod
sub new
{
  my ($class, $nbits)= @_;
  my $self= new Bit::Vector($nbits);
  bless $self, $class;
  return $self;
}
=cut
 
sub mine
{
  my $self= shift;
  my $class= ref($self) || $self;
  print "Hello\n";
}
 
1;
[download]

I am running perl version 5.6.1.

Thanks!
-toma

It should work perfectly the first time! - toma

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