Programming Perl, 4th Edition

Method Invocation Using the Arrow Operator

We mentioned that there are two styles of method invocation. The first style for invoking a method looks like this:

INVOCANT–>METHOD(LIST)
INVOCANT–>METHOD

For obvious reasons, this style is usually called the arrow form of invocation. (Do not confuse –> with =>, the “double-barrelled” arrow used as a fancy comma.) Parentheses are required if there are any arguments. When executed, the invocation first locates the subroutine determined jointly by the class of the INVOCANT and the METHOD name, and then calls that subroutine, passing INVOCANT as its first argument.

When INVOCANT is a reference, we say that METHOD is invoked as an instance method; when INVOCANT is a package name, we say that METHOD is invoked as a class method. There really is no difference between the two, other than that the package name is more obviously associated with the class itself than with the objects of the class. You’ll have to take our word for it that the objects also know their class. We’ll tell you in a bit how to associate an object with a class name, but you can use objects without knowing that.

For example, to construct an object using the class method summon and then invoke the instance method speak on the resulting object, you might say this:

$mage = Wizard–>summon("Gandalf");  # class method
$mage–>speak("friend");             # instance method

The summon and speak methods are defined by the Wizard class—or one of the classes from which it inherits. But you shouldn’t worry ...