in reply to Re: •Re: "for" surprise
in thread "for" surprise

Relying on the fact that the loop iterator has a defined value after leaving the loop is bad style in many languages, as many languages explicitly state the value of the loop iterator as undefined.

Personally, I prefer to create loop iterators that are scoped only to the loop block, as that completely avoids the issue:

for my $i (1..67) {
  ...
};

[download]

That way, $i can't be used outside the loop, and I consider that a good thing. But why are you using a loop over a fixed range instead of a loop from 1 to $end anyway?

perl -MHTTP::Daemon -MHTTP::Response -MLWP::Simple -e ' ;    # The  
$d = new HTTP::Daemon and fork and getprint $d->url and exit;#spider
($c = $d->accept())->get_request(); $c->send_response( new   #in the
HTTP::Response(200,$_,$_,qq(Just another Perl hacker\n))); ' #  web

[download]

Replies are listed 'Best First'.
Re: Re: Re: •Re: "for" surprise
by fletcher_the_dog (Friar) on Nov 21, 2003 at 20:26 UTC 
    That way, $i can't be used outside the loop, and I consider that a goo
+d thing.

    [download]
    I agree that makes sense and I do it myself all the time, but sometimes it might not be what you want to do and it might not be good thing in which case even if you think you are changing the behavior, you are not. 
    But why are you using a loop over a fixed range instead of a loop from
+ 1 to $end anyway?

    [download]
    It was a small example not real code. Where it says "# do some useful stuff" there would be ... some useful stuff :-)
[reply]
[d/l]
[select]
      ...or, for that matter, why we have: 
      for ($i=0; $i<53; $i++) {
}

      [download]
      loops, as well. Even though perl's list-iterating for-loops are incredibly sweet, and replace 99% of for-loops written in other languages, there's still that 1% of iterating loops that aren't list-iterating loops... and that's why perl still has for( ; ; ) loops as well.

      The real reason why the value is localized within the loop is that it is not the variable (by the same name) outside of the loop. Period. What it is, though, is an alias to the item in the list being iterated over. That is why you can do things like: 

      foreach my $item (@list) {
    $item = mutate $item;
}

      [download]
      and it produces the same result as: 
      @list = map { mutate $_ } @list;

      [download]
      That is... in the nth iteration of the loop, the list-iterator variable IS the nth item in the array. They are one and the same.

      With that context in mind, ask yourself how much sense it would make that your list iterator variable was not localized.


      ------------
      :Wq
      Not an editor command: Wq
[reply]
[d/l]
[select]
      but sometimes it might not be what you want to do
      That's why we have a while as well.

      Abigail

[reply]

In Section Seekers of Perl Wisdom