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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