The document is using the word "named" in the sense of "specified in the calling statement". You can take the keys of an anonymous hash:

use strict;
use warnings;
my @Uniq = uniq('a', 'b', 'c', 'a', 'b', 'a');
print "@Uniq\n";
sub uniq {
    return keys %{{map {$_=>1} @_}};
}

OUTPUT:
c a b
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Edit: Revised example to be more like the original problem.