Hi,

I'm writing up a class that needs to create a multi-dimensional array on the fly. The dimension is specified through an argument to the new() method.

The only way I can think of is to create a string of Perl code on the fly, and eval() it. Something like this:

my $dim  = 3;
my @size = (4, 5, 6);
my $var  = 'a';
my $str  = '';

for my $i (0 .. $dim - 1) {
  $str .= '  ' x $i .
          "for my \$$var (0 .. $size[$i] - 1) {\n";
  $var++;
}

$var = 'a';
$str .= '  ' x $dim . '$array' .
        join '' => map {'[$ ' . $var++ . ']'} 1 .. $dim;
$str .= " = 0;\n";

$str .= "  " x ($dim - $_) . "}\n" for 1 .. $dim;
[download]

This results in $str holding:

for my $a (0 .. 4 - 1) {
  for my $b (0 .. 5 - 1) {
    for my $c (0 .. 6 - 1) {
      $array[$ a][$ b][$ c] = 0;
    }
  }
}
[download]

This solution strikes me as rather elegant, but somewhat inefficient, but I can live with that since I need to eval this only once. Now, my main concern is how I would set individual elements (through a call to another method).

I could only think of the same approach: Create a sub on the fly that can be called with the proper arguments. Something like:

  my $i = 0;
  my $sub = 'sub { $array' .
            join '' => map {'[$_[' . $i++ . ']]'} 1 .. $dim;
  $sub .= ' = $_[-1] }' . "\n";
[download]

Now $sub looks like this:

sub { $array[$_[0]][$_[1]][$_[2]] = $_[-1] }
[download]

which I can eval and then call anonymously with the coordinates and the desired value. But, I will need to call this sub a huge number of times and hence think it will be rather inefficient.

Is there a better way?
Thanks,
--Ala

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