Nested (ARRAY|HASH)

narainhere has asked for the wisdom of the Perl Monks concerning the following question:

Request fellow monks to have a look at the following code,

use strict;
use warnings;
my @arr=(12,13,14);
my %hash=(
        "outer"=>(
            "cool"=>1,
            "Kewl"=>2,"odd"
        )
);
print keys %hash,"||",values %hash,"  ",$hash{"2"};
[download]

Though the right way to declare is like

my %hash=(
        "outer"=>{
            "cool"=>1,
            "Kewl"=>2,
        }
);
[download]

I am intrigued after looking at the o/p.How come the supposed to be keys "cool","kewl" became values and values 1,2 became keys.What exactly is the effect of using '()' in-place of '{}'

The world is so big for any individual to conquer

Comment on Nested (ARRAY\|HASH) Select or Download Code

Replies are listed 'Best First'.
Re: Nested (ARRAY\|HASH) by bart (Canon) on Oct 30, 2007 at 06:19 UTC
You could say the parens are mostly ignored, here (they just influence operator precedence — between only commas, so no effect there), not induce grouping. Perl simply flattens the list. So your first example is equivalent to `my %hash=( "outer"=> "cool"=>1, "Kewl"=> 2,"odd" );` [download] which is a fancy way of writing `my %hash=( "outer", "cool", 1, "Kewl", 2,"odd" );` [download] You can witness this flattening of the list by passing your construct as parameters to a sub and have it check what it received: `use Data::Dumper; sub test { print Dumper \@_; } test( "outer"=>( "cool"=>1, "Kewl"=>2,"odd" ) );` [download] Result: `$VAR1 = [ 'outer', 'cool', 1, 'Kewl', 2, 'odd' ];` [download]	[reply] [d/l] [select]
Re^2: Nested (ARRAY\|HASH) by narainhere (Monk) on Oct 30, 2007 at 06:38 UTC
Many Thanks BART!! The world is so big for any individual to conquer	[reply]
Re: Nested (ARRAY\|HASH) by Zaxo (Archbishop) on Oct 30, 2007 at 09:04 UTC
Bart is completely correct, but there is an organizing principle he didn't mention. The values in a hash must be scalars. To make a hash of arrays, the array values should have square braces to produce a reference. To make a hash of hashes, curlies. Each case is based on the top hash value being a scalar. After Compline, Zaxo	[reply]
Re: Nested (ARRAY\|HASH) by naikonta (Curate) on Oct 30, 2007 at 16:51 UTC
I like how bart explains it, I just wanted to let you know that the B::Deparse module helps to reveal your real structure, unlikely what you want :-) `$ perl -MO=Deparse 647981.pl use warnings; use strict 'refs'; my(@arr) = (12, 13, 14); my(%hash) = ('outer', ('cool', 1, 'Kewl', 2, 'odd')); print keys %hash, '\|\|', values %hash, ' ', $hash{'2'}; 647981.pl syntax OK` [download] Open source softwares? Share and enjoy. Make profit from them if you can. Yet, share and enjoy!	[reply] [d/l]
Re: Nested (ARRAY\|HASH) by jethro (Monsignor) on Oct 30, 2007 at 20:21 UTC
One small detail should make this quite clear: '=>' is only syntactic sugar (i.e. an alias) for ','. Change all '=>' to ',' and it immediately becomes apparent that there is no subhash.	[reply]