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 %unique = map { $_ => 1 } qw( one two one two three four! );

To print it:

 print join ", ", sort keys %unique;

To add values to it:

 $unique{$_}=1 foreach qw( one after the nine oh nine );

To remove values:

 delete @unique{ qw(oh nine) };

To check if a value is there:

 $unique{ $value };        # which is why I like to use "1" as my value

(thanks to Gaal Yahas for the above examples)

There are three drawbacks I see:

=over 4

=item 1) You type more.

=item 2) Your reader might not understand at first why did you use hash 
    and what will be the values.

=item 3) You lose the order.

=back

Usually non of them is critical but when I saw this the 10th time
in a code I had to understand with 0 documentation I got frustrated.


=item 3) using Array::Unique

So I decided to write this module because I got frustrated
by my lack of understanding what's going on in that code
I mentioned.

In addition I thought it might be interesting to write this and
then benchmark it.

Additionally it is nice to have your name displayed in 
bright lights all over CPAN ... or at least in a module.

Array::Unique lets you tie an array to hmmm, itself (?)
and makes sure the values of the array are always unique.

Since writing this I am not sure if I really recommend its usage.
I would say stick with the hash version and document that the
variable is aggregating a unique list of values.


=item 4) Using real SET

There are modules on CPAN that let you create and maintain SETs.
I have not checked any of those but I guess they just as much of
an overkill for this functionality as Unique::Array.


=back

=head1 BUGS

 use Array::Unique;
 tie @a, 'Array::Unique';

 @c = @a = qw(a b c a d e f b);
 
 @c will contain the same as @a AND two undefs at the end because
 @c you get the same length as the right most list.

=head1 TODO

Test:

Change size of the array
Elements with false values ('', '0', 0) 

   splice:
   splice @a;
   splice @a,  3;
   splice @a, -3;
   splice @a,  3,  5;
   splice @a,  3, -5;
   splice @a, -3,  5;
   splice @a, -3, -5;
   splice @a,  ?,  ?, @b;



Benchmark speed

Add faster functions that don't check uniqueness so if I 
know part of the data that comes from a unique source then
I can speed up the process,
In short shoot myself in the leg.

Enable optional compare with other functions

Write even better implementations.

=head1 AUTHOR

Gabor Szabo <gabor@pti.co.il>

=head1 LICENSE

Copyright (C) 2002-2008 Gabor Szabo <gabor@pti.co.il>
All rights reserved.  http://www.pti.co.il/

You may distribute under the terms of either the GNU 
General Public License or the Artistic License, as 
specified in the Perl README file.

No WARRANTY whatsoever.