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]

---

---

Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!

Titles consisting of a single word are discouraged, and in most cases are disallowed outright.

Read Where should I post X? if you're not absolutely sure you're posting in the right place.

Please read these before you post! —

• How do I compose an effective node title?
• How do I post a question effectively?
• Markup in the Monastery

Posts may use any of the Perl Monks Approved HTML tags:

a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr

You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)

	For:		Use:
	&		&
	<		&lt;
	>		&gt;
	[		&#91;
	]		&#93;

Link using PerlMonks shortcuts! What shortcuts can I use for linking?

See Writeup Formatting Tips and other pages linked from there for more info.