How can I get a working Data::Alias in Perl 5.12?

Question

I like Data::Alias. It seems to be broken in 5.12. Can it be fixed? Will it be fixed soon? Is there any nice alternative?

Answer 1

I suggest filing a bug on CPAN. If someone sees the problem, it's much more likely to be fixed.

In fact, it looks like someone else has seen this problem, too! I suggest hitting up the Perl 5 Porters mailing list, and seeing if anyone there can help.

As an interesting side note, it seems like being able to do aliases may be coming to Perl as a language feature in the future, with the cleanup of := no longer meaning an empty attribute list. Look forward to it! :)

Answer 2

The module hasn't been updated since 2007 but you can always send a message to the author (Matthijs van Duin: [email protected]) or file a bug report as Robert mentioned in his answer.

Here are some alternatives:

• As far as additional CPAN modules for aliasing that work in 5.12+:

  • Variable::Alias - clean syntax
  • Tie::Alias - a pure perl solution
  • Lexical::Alias - clean syntax
  • Devel::LexAlias - a bit lower level

  And searching for 'alias' on CPAN turns up a few more, none seem to provide the "do everything with aliases in this statement" feature of Data::Alias though. So until Data::Alias is fixed, you can use one of the above, or the following pure Perl methods:

• Perl has built in support for aliasing any variable to variables that exist in the symbol table. This is done as follows:

  my $x = 1;
  our $y; # declare $y in the symbol table for the current package
  {
      local *y = \$x;  # make $y an alias of $x in the current scope
      $y++;
  }
  print $x;  # prints 2
  

  But as always, be aware of what dynamic scope / local actually does before using it.

• A lexical scalar can be used as an alias within the scope of a for loop:

  my $x = 1;
  for my $y ($x) {
      $y++;
  }
  print $x;  # prints 2
  

  this type of lexical alias can even be passed out of the loop in a closure if needed

• You can create array aliases using Perl's aliasing magic for subroutine argument lists:

  my $x = 1;
  my $alias = sub{\@_}->($x); # return a reference to its argument list, 
                              # which maintains its aliases
  $$alias[0]++;
  print $x;     # prints 2
  

  but that doesn't really give you any more functionality than references, just with a different syntax.

• And an example using Perl's references:

  my $x = 1;   
  my $y = \$x;  # take a reference to $x
  $$y++;        # dereference $y
  print $x;     # prints 2 
  

Answer 3

I just found another potential option: Scalar::Alias, which seems to work in Perl 5.12. Obviously, it only aliases scalars, but it doesn't require a fat comma in place of an equals sign.