What is $x{$y}?

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

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Re: What is $x{$y}? by toolic (Bishop) on Sep 10, 2012 at 19:04 UTC
See also: perlref perlreftut References quick reference	[reply]
Re: What is $x{$y}? by Riales (Hermit) on Sep 10, 2012 at 19:02 UTC
~~It looks like you have a array `@x` of array refs, of which you want the array ref at index `$y`.~~ You have a hash `%x` of array refs, of which you want the array ref with key `$y`. The `@{ }` that surrounds all of it means you're dereferencing the array ref at index `$y` and getting the array that the array ref points to.	[reply] [d/l] [select]
Re^2: What is $x{$y}? by dave_the_m (Monsignor) on Sep 10, 2012 at 19:12 UTC
Or strictly speaking, a hash `%x` of array refs. Dave.	[reply] [d/l]
Re^3: What is $x{$y}? by Riales (Hermit) on Sep 10, 2012 at 19:16 UTC
Oops, you're right. Array is totally wrong. Making the change to the original post!	[reply]
Re^4: What is $x{$y}? by invaderzard (Acolyte) on Sep 10, 2012 at 23:59 UTC
Re^5: What is $x{$y}? by AnomalousMonk (Archbishop) on Sep 11, 2012 at 00:30 UTC
Re: What is $x{$y}? by Rudolf (Pilgrim) on Sep 10, 2012 at 19:44 UTC
Like it was said above, it is a dereference because a hash only holds scalar values which could be references to an array, hash, or another scalar.. any reference. $x{$y} grabs the reference which is your scalar that you must dereference to make sense out of it. Just like my $ref = \@ary; creates a reference to the array and the way you would dereference it would be either @$ref or @{$ref}. In the case of a complex variable such as $x{$y} it is probably easier and more readable (once you get used to it) to use surrounding curly braces.	[reply]
Re: What is $x{$y}? by invaderzard (Acolyte) on Sep 10, 2012 at 23:58 UTC
Thanks guys. Just one more question. What about $x{@y}?	[reply]
Re^2: What is $x{$y}? by AnomalousMonk (Archbishop) on Sep 11, 2012 at 00:22 UTC
In the `$x{ @y }` expression, array `@y` is being evaluated in scalar context, i.e., it yields the number of elements of the array. This number is then stringized as a key for the hash. `>perl -wMstrict -le "my %hash = qw(one uno two dos); my @y = 5 .. 8; ;; print 'scalar @y: ', scalar @y; print 'does not exist' if not exists $hash{ @y }; ;; $hash{ '4' } = 'four'; print 'does exist: ', qq{'$hash{ @y }'} if exists $hash{ @y }; " scalar @y: 4 does not exist does exist: 'four'` [download]	[reply] [d/l] [select]
Re^2: What is $x{$y}? by Anonymous Monk on Sep 11, 2012 at 00:03 UTC
Just one more question. What about $x{@y}? You tell us? Try It To See? Tutorials: Basic debugging checklist? I don't know what this means, do you have any idea? `$ perl -MData::Dump -e " @x = 1..2; $y{@x} = @x; dd \%y " { 2 => 2 } $ perl -MData::Dump -e " @x = 1..4; $y{@x} = @x; dd \%y " { 4 => 4 }` [download]	[reply] [d/l]