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

$Id: Lock.pm,v 0.2 2008/06/27 19:50:52 dankogai Exp dankogai $

   use Data::Lock qw/dlock dunlock/;

   # note parentheses and equal

   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.

The only exception is objects. It does NOT lock its internals and for good reason.

Suppose you have a typical class like:

  package Foo;
  sub new     { my $pkg = shift; bless { @_ }, $pkg }
  sub get_foo { $_[0]->{foo} }
  sub set_foo { $_[0]->{foo} = $_[1] };

And

  dlock( my $o = Foo->new(foo=>1) );

You cannot change $o but you can still use mutators.

  $o = Foo->new(foo => 2); # BOOM!
  $o->set_foo(2);          # OK

If you want to make $o->{foo} immutable, Define Foo::new like:

  sub new {
      my $pkg = shift; 
      dlock(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()

  dlock($scalar);

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

Does the opposite of dlock.

Readonly, perlguts, perlapi

Dan Kogai, <dankogai at dan.co.jp>

See Attribute::Constant.

Copyright 2008 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.