The next is the inappropriate use of grep and map. grep seems to be the ideal subject for abuse. Lots of people seem to think of it as an 'element finder'. Uh, No. Its a filter. The idea is for it to be used on lots of elements to find subsets of the original elements, normally more than one. There are _much_ more efficient ways of finding a single element in an array. map() is abused in a similar way. It is NOT a for loop. Ok, if you're writing an obfu, or you _really_ dont care about speed then fine use map or grep. But its a piece of shorthand that should be used only rarely, that is when you need to transform most elements from one array into a different set of elements in a new array. Incidentally if you decide to use map or grep in void context then grep seems to be faster.

So heres what to keep in mind:

• Stay away from the 3 arg for loop. This actually is dealt with by perl as while(){}continue{} and accordingly has the overhead of creating two scoped blocks added in. Its very slow.
• If you must use the 3 arg for loop (loop from $highest to $lowest) *only* use the first two args. Perl is mart enough to convert these into while(){} and avoid the extra continue block.
• Map is a tranform function. Dont use it instead of a for loop unless you actually need to apply a function to each and every element in a loop. If you want to use it in void context then grep will probably be faster.
• Grep is a filter. Dont use it if you are looking for only one element. But for some reason its faster than map.
• If you dont need a scoped block then try to write looping code without it using modifiers. Creative use of the logical operators and the comma operator come in use here.
• for (LIST) is basically speaking the most efficient way to iterate. This includes the use of the '..' construct

use Benchmark 'cmpthese';

our $n=10;
our $sum=0;

cmpthese (-5,{
              'grep{}'    => '$sum=0; grep {$sum+=$_} 0..$n;',
              'grep()'    => '$sum=0; grep ($sum+=$_,0..$n);',
              'map{}'     => '$sum=0; map {$sum+=$_} 0..$n;',
              'map()'     => '$sum=0; map ($sum+=$_,0..$n);',
              'for_modif' => '$sum=0; $sum+=$_ foreach 0..$n;',
              'foreach'   => '$sum=0; foreach my $i (0..$n) {$sum+=$i}
+',
              'for(;;)3'  => '$sum=0; for (my $i=0;$i<=$n;$i++) {$sum+
+=$i}',
              'for(;;)2'  => '$sum=0; for (my $i=0;$i++<=$n;) {$sum+=$
+i}',
              'w{}c{}'    => '$sum=0; my $i=0; while($i<=$n){$sum+=$i}
+continue{$i++}',
              'while'     => '$sum=0; my $i=0; while($i<=$n){$sum+=$i+
++};',
             });
__END__
#last two columns removed for space reasons
             Rate map{} grep{} map() for(;;)3 w{}c{} grep() for(;;)2 w
+hile 
map{}     39416/s    --    -3%  -21%     -34%   -34%   -41%     -45%  
+-47% 
grep{}    40750/s    3%     --  -18%     -32%   -32%   -39%     -44%  
+-46% 
map()     49897/s   27%    22%    --     -16%   -17%   -25%     -31%  
+-33% 
for(;;)3  59526/s   51%    46%   19%       --    -0%   -11%     -18%  
+-21% 
w{}c{}    59804/s   52%    47%   20%       0%     --   -10%     -17%  
+-20% 
grep()    66614/s   69%    63%   34%      12%    11%     --      -8%  
+-11% 
for(;;)2  72308/s   83%    77%   45%      21%    21%     9%       --  
+ -4% 
while     75007/s   90%    84%   50%      26%    25%    13%       4%  
+  -- 
foreach   80124/s  103%    97%   61%      35%    34%    20%      11%  
+  7% 
for_modif 84073/s  113%   106%   68%      41%    41%    26%      16%  
+ 12%
[download]

Anyway, I suppose this is a bit of a rant, but its something that has gotten to me a bit lately, especially respected members of our community posting what I consider to be 'clever but BS' solutions to problems. To me if a solution is not as effecient as is reasonable then it shouldnt be posted.

:-)