undef vs. $foo = 0

DaWolf has asked for the wisdom of the Perl Monks concerning the following question: ⭐ (input and output)

Wich one is the best way to reset a variable?

1st method:

foreach $foo(@foo)
{
  undef $bar;
  ...
  $bar = $some + $thing;
}
[download]

2nd method:

foreach $foo(@foo)
{
  $bar = 0;
  ...
  $bar = $some + $thing;
}
[download]

TIA, DaWolf

Originally posted as a Categorized Question.

Comment on undef vs. $foo = 0 Select or Download Code

Replies are listed 'Best First'.
Re: undef vs. $foo = 0⭐ by ariels (Curate) on May 02, 2002 at 14:39 UTC
One sets the variable to undef, the other to 0. They're not equivalent. "Resetting" a variable is probably more like `undef $bar`. But which you want probably depends on what it is you want to do. For some applications, you'd set `$bar=0` initially (or `$bar=''` for others), so that could be useful. Example To print the sum of the numbers in an array, `my $sum; # ... $sum = 0; $sum += $_ for @array; print "Sum is $sum\n";` [download] Using `undef $sum` would be a somewhat subtle error in this case. Other times, you want `undef`inedness, and you `undef` things accordingly. Which is right to use depends on what is "right".	[reply] [d/l] [select]
Re: undef vs. $foo = 0 by crazyinsomniac (Prior) on May 03, 2002 at 05:11 UTC
The best method is `foreach $foo(@foo) { $bar = $some + $thing; }` [download] no need for an intermediary step unless you're doing something with $bar. If $bar has a default value, set it to that value, otherwise undef.	[reply] [d/l]
Re: undef vs. $foo = 0 by Mur (Pilgrim) on May 06, 2002 at 14:29 UTC
undef $bar may have some useful side-effects, if $bar is an object. `$bar = Foo->new(); ... undef $bar;` [download] will invoke "Foo::DESTROY", if it is defined. `$bar = 0;` [download] will also invoke DESTROY, but not if '0' is a valid assignment in the "Foo" class (long shot, I know).	[reply] [d/l] [select]
Re: undef vs. $foo = 0 by Mur (Pilgrim) on May 06, 2002 at 14:58 UTC
undef $bar may have some useful side-effects, if $bar is an object. `$bar = Foo->new(); ... undef $bar;` [download] will invoke "Foo::DESTROY", if it is defined. `$bar = 0;` [download] will also invoke DESTROY, but not if '0' is a valid assignment in the "Foo" class (long shot, I know). Originally posted as a Categorized Answer.	[reply] [d/l] [select]

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