NAME

Attribute::Tie - Tie via Attribute

SYNOPSIS

  use Attribute::Tie;
  my %hash   : Tie('Hash::Yours', args ...);
  my @array  : Tie('Array::Yours', args ...);
  my $scalar : Tie('Scalar::Yours', args ...);

DESCRIPTION

Attribute::Tie allows you to tie variables via attribute. This is more intuitive than

  tie my %hash, "Tie::Hash::Yours", args ... or die "$!";

The first argument to Tie() is the name of the module to which you want to tie the variable. You can omit 'Tie' therein.

  my %db  : Tie('DB_File', ....); # ties to DB_File;
  my @fie : Tie('File', ...);     # ties to Tie::File;

You do not have to use Tie::Whatever; Attribute::Tie does it for you.

Attribute::Tie vs Attribute::Handlers' autotie

I wrote this module for two reasons:

semantics

Attribute::Handlers offers an alternate approach via autotie. That looks like this.

  use Attribute::Handlers autotie => { File => 'Tie::File' };
  my @array : File('array.txt');

Which is handy but it hides the fact that the variable is actually tied. I want the attribute name to reflect what is really done to the variable.

error handling

unlike most attributes, tie-ing variable may fail. This is especially true for modules that tie variables to external files. But autotie does not trap the error; it just leaves the variable untied. Consider this.

  use Attribute::Handlers autotie => { File => 'Tie::File' };
  my @array : File('/nonexistent/nowhere.txt');

Of course you can check the error like this.

  tied(@array) or die $!

or this:

  my @array : File('/nonexistent/nowhere.txt') or die $!;

First one is error-prone and the second one is unnatural because setting attribute is not assignment. When the error happens, it should croak before the attribute is 'set', or fails to be set.

On the other hand, Attribute::Tie dies on failure by default.

  my @array : Tie('File', '/nonexistent/nowhere.txt');
  # you die here!

CUSTOM ERROR HANDLER

By default, Attribute::Tie dies on failure as follows.

  tie(%HASH, 'SDBM_File', ./_none_/db, 514, 438) failed : 
  No such file or directory at t/04-error.t line 12

You can change this behavior via Attribute::Tie->seterror().

  # sets the error handler
  Attribute::Tie->seterror(sub{ die @_ });

  # disables error handling like Attribute::Handler's autotie
  Attribute::Tie->seterror(sub{});

   Attribute::Tie->seterror(0);
  # restores default handler
  Attribute::Tie->seterror(1);

EXPORT

None by default.

SEE ALSO

perltie, Attribute::Handlers

AUTHOR

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

COPYRIGHT AND LICENSE

Copyright (C) 2006 by Dan Kogai

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself, either Perl version 5.8.8 or, at your option, any later version of Perl 5 you may have available.