The cookbook (and this site) provide a small algorithm for shuffling array elements in place. It contains two constructs I have not seen and can't place, so I seek help in understanding these:

The code looks like this:

for ($i = @$array; --$i; ) {
  my $j = int rand ($i+1);
  next if $i == $j;
  @$array[$i,$j] = @$array[$j,$i]
}

[download]
My 2 questions:

1) in the for loop: I see a predecrement where a guard should be. what's with that? I understand C-style for loops to be
for(init..; guard..; increment/decrement) {..}

2) $array is a reference to a 1-D array, yet the last line here uses indices appropriate for a 2-D array. Why does this work and how?

Nuggets of wisdom would be dearly appreciated.

In reply to help in understanding the standard array shuffle by Anonymous Monk

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