How to "unlink" a Perl array reference from the referenced variable?

Question

In Perl 5.10.1:

#!/usr/bin/perl

my @a = (1, 2, 3);
my $b = \@a;
print join('', @{$b}) . "\n";
@a = (6, 7, 8);
print join('', @{$b}) . "\n";

This prints 123 then 678. However, I'd like to get 123 both times (i.e. reassigning the value of @a will not change the array that $b references). How can I do this?

Obligatory warning: Do not use variables named $a or $b in general Perl code. $a and $b are globals used by the sort function and they will be overwritten if sort gets called by your code or by any module it uses. (Yes, I realize that declaring them lexically (with my) sidesteps that because you're not using the global version then, but it's still asking for trouble to use $a or $b.) — Dave Sherohman
– Dave Sherohman, Commented Jun 25, 2010 at 10:22

mob · Accepted Answer · 2010-06-24 15:48:42Z

3

Make a reference to a copy of @a.

my $b = [ @a ];

answered Jun 24, 2010 at 15:48

mob

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4 Comments

james Over a year ago

Great, thanks. Similarly, my $b = { %a }; works with hashes. I notice that no similar trick is needed for code references though - why is that?

james Over a year ago

I'm basically doing my $a = sub { ... }; my $b = $a;. Then when I reassign $a to a different coderef, $b doesn't change (which is the behavior I want; I was just wondering why that happens).

hobbs Over a year ago

Because $b isn't a reference to $a. When you do $a = sub { ... } later on, you're creating a new coderef and putting it in $a -- which doesn't replace the thing that $b points to. The difference here is that a coderef is always a ref -- you never work with non-ref "code values".

Oesor Over a year ago

Note that if @a contains references, this will still have a reference to the original data in $b. For complex data structures you should use something like Storable's clone.

Gerrit · Accepted Answer · 2010-06-24 22:52:10Z

0

Bretter use dclone for deep cloning of references pointing to anonymous data structures.

answered Jun 24, 2010 at 22:52

Gerrit

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