my %seen;
my @uniq = grep { ! $seen{$_} ++ } @arr;

##</code><code>##

use strict;
use warnings;

use Benchmark q{cmpthese};

my @arr = ( q{a} .. q{z} ) x 1000;

cmpthese(
   -10,
   {
       useGrep  => sub
          {
              my %seen;
              return grep { ! $seen{$_} ++ } @arr;
          },
       useSlice => sub
          {
              my %seen;
              @seen{@arr} = ();
              return keys %seen;
          },
   });

##</code><code>##

           Rate  useGrep useSlice
useGrep  13.0/s       --     -63%
useSlice 35.2/s     172%       --