The only thing that occurs to me though is that fingerprinting the whole object shouldn't be necessary - it should be sufficient to fingerprint an ordered, delimited concatenation of selected instance fields. It is more usual (though not necessarily mandatory) for this to be the primary key in the logical data model rather than some bulk data field.

Update: You could also consider storing the MD5 in the database, setting a UNIQUE constraint on some selection of fields and letting the database deal with the problem.

Data::Dumper won't guarantee a unique key ordering

oh, it does =)
just set $Data::Dumper::Sortkeys to 1

Of course, you might want to do a bit more data analysis before you just jump into using a hash, since the process of creating the hash will, by definition, take longer than it would to simply examine the two structures once. So whether or not the hash will speed up your code depends on what you want to do with it.

That said, MD5 is a good hashing algorithm. The number of false collisions is small, the algorithm itself is fairly simple (and fast) and if your structure is significantly bigger than the hash key size, the process of comparing many hash keys might be a lot faster than that of comparing many structures. We use it where I work to shortcut the parsing of some multi-megabyte structures, if the user asks to include them many times.

It seems using Digest::MD5 is the way to go, however I see a big difference between taking a MD5 from an Object or a file.
For example, you might not want to use all the data from the objects for the fingerprint!

LuCa

I would use Data::UUID to generate a universal unique identifier during object creation; you would store that object identifier and use it later for comparison; in fact there is no reason to compute object fingerprint later.

package Class;

use strict;
use warnings;

use Data::UUID;

sub new {
  my $class = shift;

  my $uuid = Data::UUID->new;

  return bless {
    some => 'data',
    object_signature => $uuid->create_str(),
  }, $class;
}

sub object_signature { shift->{object_signature}; }

1;
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