Re: hash references

Assigning undef to a hash doesn't "destroy" the hash. I t just empties it.

my %h = (1, 2);
print bless(\%h), $/;
%h = undef;
print bless(\%h), $/;
__END__
main=HASH(0x99ae63c)
main=HASH(0x99ae63c)
[download]

It's the same memory address after assigning undef.

The usual way to do it is to declare the hash inside the loop:

for $val (@variables) {
   my %temp;
   # work with %temp here;

   push @array, \%temp;
}
[download]

That way a new variable is generated for each iteration.

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Re^2: hash refferences by leonidlm (Pilgrim) on Aug 21, 2008 at 12:36 UTC
But whats the difference between the following: 1. Declaration of the %temp inside the loop 2. Performing: undef %temp at the end of each iteration Someone ?	[reply]
Re^3: hash refferences by Corion (Patriarch) on Aug 21, 2008 at 12:40 UTC
They are completely different. `undef %temp` empties the variable but still keeps the variable there, while a lexical variable goes out of scope. The `undef %temp` acts on the values, while leaving the scope acts on the binding of the name to the value.	[reply] [d/l] [select]
Re^3: hash references by moritz (Cardinal) on Aug 21, 2008 at 12:53 UTC
What Corion said is right. `%temp` is actually a container - think of a bucket. You can fill this container (putting water into the bucket), and empty it, which is what `%temp = undef` does. Or you can but your bucket into the cupboard, (pushing it to an array), and take a new bucket (declaring `%temp` inside the loop). In this real-world analogy you can see that there's a huge difference between these two things.	[reply] [d/l] [select]
Re^4: hash references by Anonymous Monk on Aug 22, 2008 at 06:44 UTC
which is what %temp = undef does. No, thats what `undef %temp` does, big difference	[reply] [d/l]
Re^2: hash refferences by leonidlm (Pilgrim) on Aug 21, 2008 at 12:55 UTC
Another thing: Unfortunately I can't release the %temp variable every loop iteration, I need to perform it on demand. How I can do it ?	[reply]
Re^3: hash refferences by moritz (Cardinal) on Aug 21, 2008 at 12:58 UTC
`push @array, { %temp };` That actually copies the items from `%temp` into an anonymous hash, and returns its reference. See perlreftut and perlref for more details.	[reply] [d/l] [select]
Re^4: hash refferences by leonidlm (Pilgrim) on Aug 21, 2008 at 13:15 UTC
Heh thanks, this is exactly what I did, but somehow it seems not efficient enough. What about the following solution: Substitute the %temp variable by $tempRef= {} ?	[reply]
Re^5: hash refferences by moritz (Cardinal) on Aug 21, 2008 at 13:20 UTC
Re^3: hash refferences by Corion (Patriarch) on Aug 21, 2008 at 12:57 UTC
You can't. You can store copies of the values in another variable maybe.	[reply]