I put the and ++$i there to stop the scalar keys %hash being optimised away for being in a void context: 

[0] Perl> %a = 1..2e6; %b = 1..2e6;;

[0] Perl> cmpthese -1, { 
    A=>q[ scalar keys %a and ++$i for 1 .. 10000 ], 
    B=>q[ scalar keys %b for 1 .. 10000 ] 
};;
    Rate    A    B
A  804/s   -- -26%
B 1087/s  35%   --

[download]

A problem I've been bitten by with other useless statements in void contexts.

And because it is far cheaper than an assignment: 

[0] Perl> cmpthese -1, { 
    A=>q[ scalar keys %a and ++$i for 1 .. 10000 ], 
    B=>q[ my $x = scalar keys %b  for 1 .. 10000 ] 
};;
   Rate    B    A
B 658/s   -- -19%
A 812/s  24%   --

[download]

and therefore less of a bias to the test.

Do you have a better way to deal with these issues?

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
"Science is about questioning the status quo. Questioning authority".
In the absence of evidence, opinion is indistinguishable from prejudice.
"Too many [] have been sedated by an oppressive environment of political correctness and risk aversion."

In reply to Re^3: What is the most efficient way to see if a hash is empty? by BrowserUk
in thread What is the most efficient way to see if a hash is empty? by ELISHEVA

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