++, -- (both pre and postfix versions), -= and += are exempt from that warning precisely because of this common use: 

perl -Mstrict -w -e'my $f; $f++; print "$f\n"'

[download]
prints (only) 
1

[download]
"What should it profit a man, if he should win a flame war, yet lose his cool?"

In reply to Re^3: using hashes to count by Joost
in thread using hashes to count by spiros

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