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Data::Lock - makes variables (im)?mutable


$Id:,v 1.3 2014/03/07 18:24:43 dankogai Exp dankogai $


   use Data::Lock qw/dlock dunlock/;

   dlock my $sv = $initial_value;
   dlock my $ar = [@values];
   dlock my $hr = { key => value, key => value, ... };
   dunlock $sv;
   dunlock $ar; dunlock \@av;
   dunlock $hr; dunlock \%hv;


dlock makes the specified variable immutable like Readonly. Unlike Readonly which implements immutability via tie, dlock makes use of the internal flag of perl SV so it imposes almost no penalty.

Like Readonly, dlock locks not only the variable itself but also elements therein.

As of verion 0.03, you can dlock objects as well. Below is an example constructor that returns an immutable object:

  sub new {
      my $pkg = shift;
      my $self = { @_ };
      bless $self, $pkg;

Or consider using Moose.


Like List::Util and Scalar::Util, functions are exported only explicitly. This module comes with dlock and dunlock.

  use Data::Lock;                   # nothing imported;
  use Data::Lock qw/dlock dunlock/; # imports dlock() and dunlock()




Locks $scalar and if $scalar is a reference, recursively locks referents.


Does the opposite of dlock.


Here I have benchmarked like this.

  1.  Create an immutable variable.
  2.  try to change it and see if it raises exception
  3.  make sure the value stored remains unchanged.

See t/ for details.

Simple scalar
                Rate  Readonly Attribute      glob     dlock
  Readonly   11987/s        --      -98%      -98%      -98%
  Attribute 484562/s     3943%        --       -1%       -4%
  glob      487239/s     3965%        1%        --       -3%
  dlock     504247/s     4107%        4%        3%        --
Array with 1000 entries
                Rate  Readonly     dlock Attribute
  Readonly   12396/s        --      -97%      -97%
  dlock     444703/s     3488%        --       -6%
  Attribute 475557/s     3736%        7%        --
Hash with 1000 key/value pairs
                Rate  Readonly     dlock Attribute
  Readonly   10855/s        --      -97%      -97%
  dlock     358867/s     3206%        --       -5%
  Attribute 377087/s     3374%        5%        --


Readonly, perlguts, perlapi


Dan Kogai, <dankogai+gmail at>


Please report any bugs or feature requests to bug-data-lock at, or through the web interface at I will be notified, and then you'll automatically be notified of progress on your bug as I make changes.


You can find documentation for this module with the perldoc command.

    perldoc Data::Lock

You can also look for information at:


Copyright 2008-2013 Dan Kogai, all rights reserved.

This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.