What, if any, are the benefits and dangers of using $_ within nested loops? For example:

my %cds = (
  classical => [
    [ 'Mozart', 'Requiem' ],
    [ 'Beethoven', '3rd Symphony' ]
  ],
  rock => [
    [ 'Van Halen', '1984' ]
  ],
  jazz => [
    [ 'Miles Davis', 'Birth of the Cool' ],
    [ 'Stan Getz', 'Brothers' ]
  ],
);
for( sort keys %cds ) {
  print $_, ": ", scalar @{ $cds{$_} }, " in group\n";
  for( @{ $cds{$_} } ) {
    print "\t", join(",", @{ $_ }), "\n";
  }
}

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My question concerns using $_ in the inner loop of this example. Is is possible I'll destroy the value in $_ of the outer loop by creating the second for loop? Do I even need to worry about it, since I've already used the array reference in $_ by the time I enter the inner loop? Or is there a more evil threat that the inner loop itself will become corrupt?

  # "for( ... ) { ... }" creates assignment to $_, right?
  # doesn't this 'corrupt' value for looking up $cds{$_} ?
  for( @{ $cds{$_} } ) { ... }

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And if variable scoping would solve my percieved problem, understand that the issue of my vs. local is something I don't grok yet. I completely understand my, but local escapes me.

The odd thing is that I ran something like this, with -w and use strict;, and it worked! Why? Should it have worked?

In reply to Using $_ in nested loops by t'mo

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