Re: Getting different anonymous arrays

I thought I would give it a test.
Could someone explain this?

use Data::Dumper;
use strict; 
my @array;
my %array;

@array = qw( a b c d ) ;
@array{ @array } = ( [ @array ] ) x @array ;

print Data::Dumper->Dump([\%array], ["*array"]);
__OUTPUT__
%array = (
           'c' => [
                    'a',
                    'b',
                    'c',
                    'd'
                  ],
           'a' => $array{'c'},
           'b' => $array{'c'},
           'd' => $array{'c'}
         );
[download]

I don't get it either!

perl -v

This is perl, v5.8.0 built for MSWin32-x86-multi-thread
(with 1 registered patch, see perl -V for more detail)

Copyright 1987-2002, Larry Wall

Binary build 806 provided by ActiveState Corp. http://www.ActiveState.
+com
Built 00:45:44 Mar 31 2003

---snip---
[download]

flounder

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Re: Re: Getting different anonymous arrays by broquaint (Abbot) on Sep 08, 2003 at 18:59 UTC
`( [ @array ] ) x @array ;` [download] Make N copies of `[ @array ]` `@array{ @array } = ( [ @array ] ) x @array ;` [download] Do the hash assign of the N copies. This is all obvious so far, now for the trickier bit, the output `%array = ( 'c' => [ 'a', 'b', 'c', 'd' ], 'a' => $array{'c'}, 'b' => $array{'c'}, 'd' => $array{'c'} );` [download] Unusual, you say, that the key `'c'` should get 'the original' and the rest get copies, but if we look at the ordering of the keys this makes sense `shell> perl -le 'print keys %{{map {$_=>1} qw/a b c d/}}' cabd` [download] So as you may have guessed by now `Data::Dumper`'s output shows that `'c'` just happens to look like its got 'the original' due to the ordering of the hash. In reality they all point to the same anonymous array. HTH `_________ broquaint`	[reply] [d/l] [select]
Re: Re: Getting different anonymous arrays by MidLifeXis (Monsignor) on Sep 08, 2003 at 16:57 UTC
This is just a freeze/thaw way of getting back a structure which points at the same arrayref. If you built it like this: `%array = ( 'a' => ['a','b','c','d'], 'b' => ['a','b','c','d'], 'c' => ['a','b','c','d'], 'd' => ['a','b','c','d'] );` [download] you would have four different anonymous arrays, not four refencences to the same array, as the original code created. Not sure if this answered your question, or if I even understood it, but there you go :).	[reply] [d/l]
Re^3: Getting different anonymous arrays by flounder99 (Friar) on Sep 08, 2003 at 18:38 UTC
I just thought it was weird that the anonymous array was definded as the value of the hash key 'c' and all the rest of the hash keys have a value of its reference. It seems to me that the hash key 'a' would have been defined first and the other keys would have the value of its reference. I guess it doesn't matter -- they all point to the same anonymous array reference. I see what happens. if I add this line to my original program: `print join ",", keys %array;` [download] I get an output of: `c,a,b,d` [download] So `Data::Dumper` must just take the first key it gets from `keys` point it to the anonymous array reference and then have the rest of the keys point to it. That makes sense. You learn something new every day. -- flounder	[reply] [d/l] [select]