3Re: passing information into a hash

Good question. :) For this particular case, i probably should have used your second snippet (take a reference to the array instead of copying it into a new anonymous one). Consider these:

use Data::Dumper;

my @array = qw(foo bar baz);
my %hash;

for (1..5) {
   my @array = qw(foo bar baz);
   $hash{$_} = \@array;
   undef @array;
}
print Dumper \%hash;

for (1..5) {
   my @array = qw(foo bar baz);
   $hash{$_} = [@array];
   undef @array;
}
print Dumper \%hash;
[download]

I usually stick with an explicit copy since it tends to keep me out of trouble, but there are times when you do want to take a reference, and you just have to be careful when you do.

jeffa

L-LL-L--L-LL-L--L-LL-L--
-R--R-RR-R--R-RR-R--R-RR
B--B--B--B--B--B--B--B--
H---H---H---H---H---H---
(the triplet paradiddle with high-hat)

Comment on 3Re: passing information into a hash Download Code

Replies are listed 'Best First'.
Re: 3Re: passing information into a hash by hmerrill (Friar) on Sep 29, 2003 at 17:08 UTC
I want to be clear about this - I don't quite understand yet. Does @array copy the array and then create an anonymous reference to the new array? Or does it just create a new reference to the existing @array? TIA.	[reply]
5Re: passing information into a hash by jeffa (Bishop) on Sep 29, 2003 at 19:00 UTC
Don't forget to escape square brackets, the left one is all you really need to worry about: `[@array]` Anyways ... `[@array]` copies the contents of the array into a new anonymous array reference. I think the name for the collection of those contents is called a list ... so you could say that the l-value of `[@array]` is an anymous array that contains a copy of `@array`'s list ... i think. Understanding the difference between Perl's lists and arrays can be tricky, and i often get it wrong. :/ Here is some more code to study: `#!/usr/bin/perl -l use strict; use warnings; use Data::Dumper; my @array = 0..4; my $ref1 = \@array; my $ref2 = \@array; my $copy1 = [@array]; my $copy2 = [@array]; print Dumper $ref1,$copy1; print for ($ref1,$ref2,$copy1,$copy2); undef @array; print Dumper $ref2,$copy2;` [download] jeffa L-LL-L--L-LL-L--L-LL-L-- -R--R-RR-R--R-RR-R--R-RR B--B--B--B--B--B--B--B-- H---H---H---H---H---H--- (the triplet paradiddle with high-hat)	[reply] [d/l] [select]