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undef vs. $foo = 0

( #163546=categorized question: print w/ replies, xml ) Need Help??
Contributed by DaWolf on May 02, 2002 at 14:34 UTC
Q&A  > input and output


Description:

Wich one is the best way to reset a variable?

1st method:
foreach $foo(@foo) { undef $bar; ... $bar = $some + $thing; }
2nd method:
foreach $foo(@foo) { $bar = 0; ... $bar = $some + $thing; }
TIA, DaWolf

Answer: undef vs. $foo = 0
contributed by ariels

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";
Using undef $sum would be a somewhat subtle error in this case.

Other times, you want undefinedness, and you undef things accordingly. Which is right to use depends on what is "right".

Answer: undef vs. $foo = 0
contributed by crazyinsomniac

The best method is

foreach $foo(@foo) { $bar = $some + $thing; }
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.

Answer: undef vs. $foo = 0
contributed by Mur

undef $bar may have some useful side-effects, if $bar is an object.

$bar = Foo->new(); ... undef $bar;
will invoke "Foo::DESTROY", if it is defined.
$bar = 0;
will also invoke DESTROY, but not if '0' is a valid assignment in the "Foo" class (long shot, I know).

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