Monks,
I want to know if a hash is empty. Since I'll be doing it very often, I want is to perform as fast as possible. The defined section of perlfunc says: 
if (%a_hash)   { print "has hash members\n" }

[download]
To my surprise Benchmark, says that if(keys %hash) is roughy 5 times faster than if(%hash).
Less surprisingly, it also seems that if (scalar(%hash)) and if (%hash) performs equally fast, and that if (scalar(keys %hash)) and if(keys %hash) also performs equally fast. 
#!/usr/bin/perl -sw

use strict;
use Benchmark;

our $HASHSIZE   ||= 1e3;
our $ITERATIONS ||= 1e7;

my %hash = ();

# Init hash
for (my $i=0; $i<$HASHSIZE; $i++) {
  $hash{$i} = 1;
}

timethese($ITERATIONS,
          {
           _keys => sub {
             if (keys %hash) { ; }
           },
           _scalar_keys => sub {
             if (scalar(keys %hash)) { ; }
           },
           _scalar => sub {
             if (scalar(%hash)) { ; }
           },
           _if => sub {
             if (%hash) { ; }
           },
          }
         );

__END__

=pod

=head1 NAME

  bm_hash_emptiness.pl - benchmark hash emptiness tests.

=head1 SYNOPSIS

  ./bm_hash_emptiness.pl -ITERATIONS=1e7 -HASHSIZE=1e4

=head1 RESULTS

  $ ./bm_hash_emptiness.pl -ITERATIONS=1e7 -HASHSIZE=1e4
  Benchmark: timing 1e7 iterations of _if, _keys, _scalar, _scalar_key
+s...
         _if: 14 wallclock secs (14.65 usr +  0.01 sys = 14.66 CPU)
       _keys:  2 wallclock secs ( 1.99 usr +  0.00 sys =  1.99 CPU)
     _scalar: 16 wallclock secs (15.03 usr +  0.01 sys = 15.04 CPU)
  _scalar_keys:  2 wallclock secs ( 2.40 usr +  0.00 sys =  2.40 CPU)

=head SEE ALSO

  perlfunc

=cut

[download]


Should I stick to the advice from perlfunc and use if (%hash) even when it seems to be slower than the alternative?

--
Andreas

In reply to Benchmark of hash emptiness test by andreas1234567

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