You have a good idea. The details are tripping you up.

Your code on the first call:

  1. creates @array,
  2. allocates @array,
  3. returns destroying @array as it goes out of scope

On future calls it just creates @array and starts using it. So your tests should not show any advantage.

Move the "my @array;" outside of the function so that it survives from call to call: 

{  
 my $initialized;
 my @array;
 sub example {
     unless ( $initialized) {
         $#array = $size_needed;
         $initialized++;
     }
      # fill the array
 }
}

[download]
Update follows

As soon as I submitted the above I realize that may not be what you want. You may be making this way harder than you need to.

If you need a new @array on each call. Just preallocate it each time: 

sub example {
    my @array;
    $#array = $size_needed;
    # fill array -- this is where you may save time
}

[download]

In reply to Re: array pre-allocation trick by rir
in thread array pre-allocation trick by Anonymous Monk

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