While investigating Benchmark.pm I decided to try benchmarking different sorting algorithms, and have run into trouble with my implementation of <dfn>Merge Sort</dfn>; 
sub Merge(@) {
  my @array = @_;
  MergeSort (0, $#array);
  return @array;

  sub MergeSort($$) {
    my $first = shift;
    my $last = shift;
    if ($last>$first) {
      my $mid = int(($last+$first)/2);
      MergeSort($first, $mid);
      MergeSort($mid+1, $last);
      my @b;
      
      @b = ( @array[$first..$mid], @array[reverse($mid+1..$last)] );
      my ($i, $j, $k) = (0, $last-$first, $first);
      for (; $k<=$last; $k++) {
        $array[$k] = ($b[$i]<$b[$j]) ? $b[$i++] : $b[$j--];
      }
    }
  }
}

[download]
The function works perfectly, but with warnings turned on, spits out the following:
Variable "@array" will not stay shared at ./benchmark-sort.pl line [x]
+.

[download]
Where [x] is the first line in MergeSort() which manipulates @array.

Presumably I'm doing something naive here to do with the scoping of @array, which, in slightly different circumstances, could cause errors rather than just warnings.

So, what does the warning mean, and how should I declare @array to avoid it?

In reply to Scoped Variables in a Recursive Function. by kilinrax

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