What is $x{$y}?

[invaderzard]

Some codes i read have this. @{$x{$y}}

What does $x{$y} mean? And what does adding the @ in front do? Does it convert the $x{$y} into an array?

Thanks.

[toolic]

See also:

• perlref
• perlreftut
• References quick reference

[Riales]

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.

[dave_the_m]

Or strictly speaking, a hash %x of array refs.

Dave.

[Riales]

Oops, you're right. Array is totally wrong. Making the change to the original post!

[Rudolf]

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.

[invaderzard]

Thanks guys.

Just one more question. What about $x{@y}?

[AnomalousMonk]

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'

[Anonymous Monk]

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 }