Programming Perl, 4th Edition

Using the Arrow Operator

For references to arrays, hashes, or subroutines, a third method of dereferencing involves the use of the –> infix operator. This form of syntactic sugar makes it easier to get at individual array or hash elements, or to call a subroutine indirectly.

The type of the dereference is determined by the right operand―that is, by what follows directly after the arrow. If the next thing after the arrow is a bracket or brace, the left operand is treated as a reference to an array or a hash, respectively, to be subscripted by the expression on the right. If the next thing is a left parenthesis, the left operand is treated as a reference to a subroutine, to be called with whatever parameters you supply in the parentheses on the right.

Each of these next trios is equivalent, corresponding to the three notations we’ve introduced. (We’ve inserted some spaces to line up equivalent elements.)

$  $arrayref  [2] = "Dorian";         #1
${ $arrayref }[2] = "Dorian";         #2
   $arrayref–>[2] = "Dorian";         #3

$  $hashref  {KEY} = "F#major";       #1
${ $hashref }{KEY} = "F#major";       #2
   $hashref–>{KEY} = "F#major";       #3

&  $coderef  (Presto => 192);         #1
&{ $coderef }(Presto => 192);         #2
   $coderef–>(Presto => 192);         #3

You can see that the initial sigil is missing from the third notation in each trio. The sigil is guessed at by Perl, which is why it can’t be used to dereference complete arrays, complete hashes, or slices of either. As long as you stick with scalar values, though, you can use any expression to the left ...