perl: how to understand @$ref[0]?

Question

perl question about ref.

$ref = [11, 22, 33, 44];
print "$$ref[0]" . "\n";
print "@$ref[0]" . "\n";

when i run perl -d.

DB<1> p @$ref
11223344
DB<2> p $ref
ARRAY(0x9dbf480)
DB<3> p \$$ref[0]
SCALAR(0x9dbf470)
DB<4> p \@$ref[0]
SCALAR(0x9dbf470) 

$$ref[0] stands first scalar of ARRAY(0x9dbf480).

what does mean @$ref[0]? i cannot understand.

Answer 1

$ref = [11, 22, 33, 44]; is a reference to an anonymous array.

$$ref[0] or ${$ref}[0] or $ref->[0] is dereferencing the array and retrieving the first element.

@$ref[0] or @{$ref}[0] is dereferencing the array and getting an array slice that contains only the first element.

Answer 2

First, @$ref[0] is different from \@$ref[0]. You have the former in your debug session, and the latter in your script.

Anyway, @$ref[0] means the same thing as @{$ref}[0]. If you had an array named @ref, @ref[0] would be the equivalent. It's using slice notation to get the first element of the array.

The difference between @array[$x] and $array[$x] is that in the first one you can specify more than one index and get back a collection of elements from the array, instead of just one. But if you only put one index between the brackets, you get the same result.