Sadly that doesn't appear to do what I want (though I'd love it to): the docs for $Data::Dumper::Freezer talk only about modifying the object passed in, not about a return value. And indeed, trying it (with a different name to avoid the existing Math::GMP::stringify method) shows it is called but has no effect on the Data::Dumper output:

% perl -MData::Dumper -MMath::GMP -wle '
  $Data::Dumper::Freezer = "zify";
  local *UNIVERSAL::zify = sub { warn "zify $_[0]"; $_[0]->isa("Math::
+GMP") ? "z$_[0]" : $_[0] };
  my $x = [ Math::GMP->new(1) ];
  print "x[0]=$x->[0]";
  print Dumper($x);
  print "x[0]=$x->[0]";
'
Name "UNIVERSAL::zify" used only once: possible typo at -e line 3.
x[0]=1
zify 1 at -e line 3.
$VAR1 = [
          bless( do{\(my $o = 40040032)}, 'Math::GMP' )
        ];

x[0]=1
[download]

If I change it to assign back to $_[0] instead, Dumper outputs garbage ("\undef") and the data structure is corrupted to have the new string instead of the original object:

% perl -MData::Dumper -MMath::GMP -wle '
  $Data::Dumper::Freezer = "zify";
  local *UNIVERSAL::zify = sub { warn "zify $_[0]"; $_[0]->isa("Math::
+GMP") ? "z$_[0]" : $_[0] };
  my $x = [ Math::GMP->new(1) ];
  print "x[0]=$x->[0]";
  print Dumper($x);
  print "x[0]=$x->[0]";
'
Name "UNIVERSAL::zify" used only once: possible typo at -e line 1.
x[0]=1
zify 1 at -e line 1.
$VAR1 = [
          \undef
        ];

x[0]=z1
[download]

Hi hv,

I was able to get a Dumper() that appears more meaningful (to me, at least) with:

## dumper.pl ##

use strict;
use warnings;

use Data::Dumper;
use Math::GMP;

my $x = [ Math::GMP->new(101), Math::GMP->new(203), Math::GMP->new(116
+7) ];

print Dumper("@$x");

__END__

C:\_32\pscrpt>perl dumper.pl
$VAR1 = '101 203 1167';
[download]

However, I'm not familiar with Data::Dumper and I've no idea if that's of any use to you.

Cheers,
Rob

Thanks Rob, that's essentially the sort of thing I currently need to do, but it requires knowing the exact structure to be dumped and walking it myself. I also want to distinguish between GMP objects and simple integers - particularly to spot when something that should be GMP is not or v.v. - so I'd end up needing to write most of Data::Dumper myself. I had hoped somebody would already have done that for me (and that someone here would have used it).

My CPAN-fu is minimal, but of the 2,520 matches on metacpan for 'dump', a quick scan of the first 100 threw up some maybes such as Data::Printer (which cares mostly about coloured output) and Data::Dump::Streamer (which cares mostly about structure recreatability via eval). I also spotted a cross-reference to Data::Rmap, which might offer a sane way to roll my own. I'll try some of those and see what I get.