Programming Perl, 4th Edition

The Arrow Operator

Just as in C and C++, the binary –> operator is an infix dereference operator. If the right side is a [...] array subscript, a {...} hash subscript, or a (...) subroutine argument list, the left side must be a reference^[59] to an array, a hash, or a subroutine, respectively:

$aref–>[42]               # an array dereference
$href–>{"corned beef"}    # a hash dereference
$sref–>(1,2,3)            # a subroutine dereference

In an lvalue (assignable) context, if the left side is not a reference, it must be a location capable of holding a hard reference, in which case such a reference will be autovivified for you.

$aref–>[42] = 'Huh!';       # autovivify an array in $aref
$href–>{"corned beef"} = 0; # autovivify a hash in $href

In either case, it also creates the new individual array or hash element with the assigned value. For more on this (and some warnings about accidental autovivification), see Chapter 8.

If the right side of the arrow is not one of those brackets, it’s a method call of some kind. The right side must be a method name (or a simple scalar variable containing the method name or a method reference), and the left side must evaluate to either an object (a blessed reference) or a class name (that is, a package name):

my $yogi = Bear–>new("Yogi");  # a class method call
$yogi–>swipe('picnic basket'); # an object method call

The method name may be qualified with a package name to indicate in which class to start searching for the method, or with the special package name, SUPER::, to indicate that ...